2020刷题日记
因为要准备保研，所以想刷刷百练上面的题目，同时因为百练上面题目做的人比较少，大多数哦人又是使用c++做的，所以想在网上找到Java的百练答案又比较难，这篇博客即是我的刷题日记，也当作一个Java百练题解吧，想要搜索直接在本博客ctrl+f然后输入题号搜索即可
2020.1.18
我果然还是不甘心当一个five啊，今天开始刷百练的题目
有一说一之前刷过很多leetcode，做百练还是不难，但是百练不像leetcode，不能查看代码执行错误的用例，不能自定义测试用例，这点就很难受。
总结一下Java输入Scanner的几个常用API:
- nextInt()：跳过特殊字符获取下一个整数，但是获取之后cursor会停留在本行，不会跳到下一行
- next()：获取下一个字符串，会自动跳过空格，换行符等特殊字符，cursor可以移动到下一行
- nextLine():从当前的cursor开始读到换行符，会将cursor放在下一行，如果没有换行符不可以获取字符串。
执行结果：
这是因为当读取12的时候，cursor到了12的后面换行符的前面，并没有跳到下一行，二nextLine()从当前cursor读取直到遇到换行符，所以读取了空
1001:Exponentiation
import java.math.BigDecimal;
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
while(cin.hasNext()){
BigDecimal R = cin.nextBigDecimal();
int n = cin.nextInt();
BigDecimal ans = R.pow(n);
//去掉末尾多余的0
ans = ans.stripTrailingZeros();
//不使用科学计数法
String plain = ans.toPlainString();
if (plain.startsWith("0.")){
plain = plain.substring(1);
}
System.out.println(plain);
}
}
}
2020.1.19
1088:滑雪
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
int m = cin.nextInt();
int n = cin.nextInt();
int[][] hights = new int[m][n];
for (int i = 0;i < m;i++){
for (int j = 0;j < n;j++){
hights[i][j] = cin.nextInt();
}
}
System.out.println(maxLength(hights,m,n));
}
static int maxLength(int[][] hights,int m,int n){
int[][] lengths = new int[m][n];
int max = 0;
for (int i = 0;i < m;i++){
for (int j = 0;j < n;j++){
if (lengths[i][j] == 0){
lengths[i][j] = length(hights,lengths,i,j,m,n);
max = Math.max(max,lengths[i][j]);
}
}
}
return max;
}
static int length(int[][] hights,int[][] lengths,int i,int j,int m,int n){
int length = 1;
if (i > 0 && hights[i][j] > hights[i - 1][j]){
if (lengths[i - 1][j] == 0){
lengths[i - 1][j] = length(hights,lengths,i - 1,j,m,n);
}
length = Math.max(length,lengths[i - 1][j] + 1);
}
if (i < m - 1 && hights[i][j] > hights[i + 1][j]){
if (lengths[i + 1][j] == 0){
lengths[i + 1][j] = length(hights,lengths,i + 1,j,m,n);
}
length = Math.max(length,lengths[i + 1][j] + 1);
}
if (j > 0 && hights[i][j] > hights[i][j - 1]){
if (lengths[i][j - 1] == 0){
lengths[i][j - 1] = length(hights, lengths, i, j - 1, m, n);
}
length = Math.max(length,lengths[i][j - 1] + 1);
}
if (j < n - 1 && hights[i][j] > hights[i][j + 1]){
if (lengths[i][j + 1] == 0){
lengths[i][j + 1] = length(hights, lengths, i, j + 1, m, n);
}
length = Math.max(length,lengths[i][j + 1] + 1);
}
lengths[i][j] = length;
return length;
}
}
1007:DNA排序
import java.util.*;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
int n = cin.nextInt();
int m = cin.nextInt();
cin.nextLine();
List<String> DNAs = new LinkedList<>();
for (int i = 0;i < m;i++){
DNAs.add(cin.nextLine());
}
Collections.sort(DNAs, new Comparator<String>() {
@Override
public int compare(String o1, String o2) {
return nums(o1) - nums(o2);
}
});
for (String DNA:DNAs){
System.out.println(DNA);
}
}
static int nums(String DNA){
char[] chars = DNA.toCharArray();
int numa = 0;
int numc = 0;
int numg = 0;
int numt = 0;
int len = DNA.length();
for (char ch:chars){
if (ch == 'A'){
numa++;
} else if (ch == 'C'){
numc++;
} else if (ch == 'G'){
numg++;
} else {
numt++;
}
}
int sum = 0;
for(char ch:chars){
if (ch == 'A'){
numa--;
} else if (ch == 'C'){
numc--;
sum += numa;
} else if (ch == 'G'){
numg--;
sum += numa + numc;
} else {
numt--;
sum += numa + numc + numg;
}
}
return sum;
}
}
4151:电影节
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
int n = cin.nextInt();
while (n != 0){
Movie[] movies = new Movie[n];
for (int i = 0;i < n;i++){
int start = cin.nextInt();
int end = cin.nextInt();
Movie movie = new Movie(start,end);
movies[i] = movie;
}
int index = 0;
int count = 0;
while (true){
int minend = 2000;
for (Movie movie:movies){
if (movie.getStartTime() >= index){
minend = Math.min(minend,movie.getEndTime());
}
}
if (minend == 2000){
break;
} else {
count++;
index = minend;
}
}
System.out.println(count);
n = cin.nextInt();
}
}
static class Movie{
int startTime;
int endTime;
public Movie(int startTime, int endTime) {
this.startTime = startTime;
this.endTime = endTime;
}
public int getStartTime() {
return startTime;
}
public int getEndTime() {
return endTime;
}
}
}
写一个保留六位小数的程序：
DecimalFormat format = new DecimalFormat("0.000000");
System.out.println(1.2345567777);
返回的是个字符串
2020.1.20
这个百练真是把气笑了，有时候代码就是死活提交不上去，我又想念leetcode了。
4094:秘密会谈
import java.text.DecimalFormat;
import java.util.*;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
int n = cin.nextInt();
int s = cin.nextInt();
int max = 0;
for (int i = 0;i < n;i++){
int start = cin.nextInt();
int speed = cin.nextInt();
int time = start + s / speed;
max = Math.max(max,time);
}
System.out.println(max);
}
}
4095:打字员
import java.text.DecimalFormat;
import java.util.*;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
int n = cin.nextInt();
for (int i = 0;i < n;i++){
System.out.println(nums(cin.next()));
}
}
//status 0:小写
//1：大写
static int nums(String str){
int count = 0;
int status = 0;
char[] chars = str.toCharArray();
for (char ch:chars){
if ((ch >= 'a' && ch <= 'z' && status == 0) || (ch >= 'A' && ch <= 'Z' && status == 1)){
count++;
}else if (status == 0){
status = 1;
count += 2;
} else {
status = 0;
count += 2;
}
}
return count;
}
}
4096:信号转换
import java.text.DecimalFormat;
import java.util.*;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
String str = cin.next();
char[] chars = str.toCharArray();
StringBuilder ans = new StringBuilder("");
for (char ch : chars){
if (ch == 'A'){
ans.append(1);
} else if (ch == 'B'){
ans.append(2);
} else if (ch == 'C'){
ans.append('$');
} else {
ans.append("\n");
}
}
System.out.println(ans.toString());
}
}
4097:报站
import java.text.DecimalFormat;
import java.util.*;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
int n = cin.nextInt();
String[] stations = new String[n];
for(int i = 0;i < n;i++){
stations[i] = cin.next();
}
int m = cin.nextInt();
for (int i = 0;i < m;i++){
String start = cin.next();
String end = cin.next();
int startIndex = -1;
int endIndex = -1;
int j = 0;
while(startIndex == -1 || endIndex == -1){
if (stations[j].equals(start)){
startIndex = j;
}
if (stations[j].equals(end)){
endIndex = j;
}
j++;
}
if (startIndex <= endIndex){
int k = startIndex;
while (k != endIndex){
System.out.print(stations[k]+" ");
k++;
}
System.out.println(stations[endIndex]);
} else {
int k = startIndex;
while (k != endIndex){
System.out.print(stations[k]+" ");
k--;
}
System.out.println(stations[endIndex]);
}
}
}
}
4098:第二大价值
import java.text.DecimalFormat;
import java.util.*;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
int m = cin.nextInt();
for (int i = 0;i < m;i++){
int n = cin.nextInt();
Fruit max = new Fruit(0,0,0);
Fruit second = new Fruit(0,0,0);
for(int j = 0;j < n;j++){
int id = cin.nextInt();
int a = cin.nextInt();
int b = cin.nextInt();
Fruit fruit = new Fruit(a,b,id);
if (a + b > max.getA() + max.getB()){
second = max;
max = fruit;
} else if (a + b > second.getA() + second.getB()){
second = fruit;
}
}
System.out.println(second.getId()+" "+second.getA()+" "+second.getB()+" "+(second.getA()+second.getB()));
}
}
static class Fruit{
private int a;
private int b;
private int id;
public Fruit(int a, int b, int id) {
this.a = a;
this.b = b;
this.id = id;
}
public int getA() {
return a;
}
public int getB() {
return b;
}
public int getId() {
return id;
}
}
}
分享一个很坑爹的题：
4099:队列和栈
这个题坑爹之处在于你在输出error之后，还有继续处理完这次输入的余下内容
import java.util.LinkedList;
import java.util.Queue;
import java.util.Scanner;
import java.util.Stack;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
int m = cin.nextInt();
for (int i = 0;i < m;i++){
int n = cin.nextInt();
Stack<Integer> stack = new Stack<>();
Queue<Integer> queue = new LinkedList<>();
int j = 0;
for (j = 0;j < n;j++){
String opereation = cin.next();
if (opereation.equals("push")){
int num = cin.nextInt();
stack.push(num);
queue.add(num);
} else {
if (stack.empty()){
System.out.println("error");
System.out.println("error");
while(j < n){
cin.nextLine();
j++;
}
j = 0;
break;
} else {
stack.pop();
queue.poll();
}
}
}
if (j == n){
while (!queue.isEmpty()){
System.out.print(queue.poll()+" ");
}
System.out.print("\n");
Stack<Integer> ans = new Stack<>();
while(!stack.empty()){
ans.push(stack.pop());
}
while(!ans.empty()){
System.out.print(ans.pop()+" ");
}
System.out.print("\n");
}
}
}
}
2020.1.21
4100:进程检测
import java.util.*;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
int m = cin.nextInt();
for (int i = 0;i < m;i++){
int n = cin.nextInt();
int count = 0;
Progress[] progresses = new Progress[n];
for (int j = 0;j < n;j++){
int start = cin.nextInt();
int end = cin.nextInt();
Progress progress = new Progress(start,end);
progresses[j] = progress;
}
Arrays.sort(progresses, new Comparator<Progress>() {
@Override
public int compare(Progress o1, Progress o2) {
return o1.getStartTime() - o2.getStartTime();
}
});
int left = 0;
while(left < n){
Progress progress = progresses[left];
int right = left + 1;
while (right < n){
Progress temp = progresses[right];
if (temp.getStartTime() > progress.getEndTime()){
break;
} else {
progress.setStartTime(temp.getStartTime());
progress.setEndTime(Math.min(progress.getEndTime(),temp.getEndTime()));
}
right++;
}
left = right;
count++;
}
System.out.println(count);
}
}
static class Progress{
private int startTime;
private int endTime;
public Progress(int startTime, int endTime) {
this.startTime = startTime;
this.endTime = endTime;
}
public int getStartTime() {
return startTime;
}
public int getEndTime() {
return endTime;
}
public void setStartTime(int startTime) {
this.startTime = startTime;
}
public void setEndTime(int endTime) {
this.endTime = endTime;
}
}
}
4101:晶矿的个数
import java.util.*;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
int m = cin.nextInt();
for (int i = 0;i < m;i++){
int n = cin.nextInt();
cin.nextLine();
char[][] grouds = new char[n][n];
for (int j = 0;j < n;j++){
String str = cin.nextLine();
grouds[j] = str.toCharArray();
}
int red = findRed(grouds,n);
int black = findBlack(grouds,n);
System.out.println(red+" "+black);
}
}
static int findRed(char[][] grouds,int n){
int count = 0;
for (int i = 0;i < n;i++){
for (int j = 0;j < n;j++){
if (grouds[i][j] == 'r'){
count++;
DFS(grouds,i,j,n,'r');
}
}
}
return count;
}
static int findBlack(char[][] grouds,int n){
int count = 0;
for (int i = 0;i < n;i++){
for(int j = 0;j < n;j++){
if (grouds[i][j] == 'b'){
count++;
DFS(grouds,i,j,n,'b');
}
}
}
return count;
}
static void DFS(char[][] grouds,int i,int j,int n,char target){
grouds[i][j] = '$';
if (i > 0 && grouds[i - 1][j] == target){
DFS(grouds,i - 1,j,n,target);
}
if (i < n - 1 && grouds[i + 1][j] == target){
DFS(grouds,i + 1,j,n,target);
}
if (j > 0 && grouds[i][j - 1] == target){
DFS(grouds, i, j - 1, n, target);
}
if (j < n - 1 && grouds[i][j + 1] == target){
DFS(grouds, i, j + 1, n, target);
}
}
}
4103:踩方格
这一题要找规律
import java.util.*;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
int N = cin.nextInt();
int y = 2;
int ans = 3;
for (int i = 1;i < N;i++){
int temp = y;
y = y + ans;
ans = ans + 2 * temp;
}
System.out.println(ans);
}
}
4104: 单词翻转
import java.util.*;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
String input = cin.nextLine();
char[] chars = input.toCharArray();
int len = input.length();
int left = 0;
while (left < len){
while (left < len && chars[left] == ' '){
System.out.print(' ');
left++;
}
int right = left;
StringBuilder temp = new StringBuilder("");
while (right < len && chars[right] != ' '){
temp.append(chars[right]);
right++;
}
left = right;
System.out.print(temp.reverse());
}
}
}
4106:出现两次的字符-Characters Appearing twice
import java.util.*;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
int n = cin.nextInt();
for (int i = 0;i < n;i++){
Map<Character,Integer> count = new HashMap<>();
String str = cin.next();
char[] chars = str.toCharArray();
for (char ch:chars){
if (!count.containsKey(ch)){
count.put(ch,1);
} else {
count.put(ch,count.get(ch) + 1);
}
}
for (char ch:chars){
if (count.get(ch) == 2){
System.out.println(ch);
break;
}
}
}
}
}
4139:不定方程求解
import java.text.DecimalFormat;
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
int a = cin.nextInt();
int b = cin.nextInt();
int c = cin.nextInt();
int count = 0;
for (int i = c / a;i >= 0;i--){
if ((c - a * i) % b == 0){
count++;
}
}
System.out.println(count);
}
}
4142:二分法求函数的零点
import java.text.DecimalFormat;
public class Main {
public static void main(String[] args) {
DecimalFormat format = new DecimalFormat("0.000000");
System.out.println(format.format(root()));
}
static double root(){
double left = 1.5;
double right = 2.4;
while (right - left > 0.000001){
double med = (left + right) / 2;
double val = Math.pow(med,5) - 15 * Math.pow(med,4) + 85 * Math.pow(med,3) - 225 * Math.pow(med,2) + 274 * med - 121;
if (val > 0){
left = med;
} else {
right = med;
}
}
return right;
}
}
4146:数字方格
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
int n = cin.nextInt();
int a1;
int a2;
int a3;
int max = 0;
for (a1 = n;a1 >= 0;a1 --){
for (a2 = n;a2 >= 0;a2--){
for(a3 = n;a3 >= 0;a3--){
if ((a1 + a2) % 2 == 0 && (a2 + a3) % 3 == 0 && (a1 + a2 + a3) % 5 == 0){
max = Math.max(max,a1 + a2 + a3);
}
}
}
}
System.out.println(max);
}
}
4151:电影节
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
int n = cin.nextInt();
while (n != 0){
Movie[] movies = new Movie[n];
for (int i = 0;i < n;i++){
int start = cin.nextInt();
int end = cin.nextInt();
Movie movie = new Movie(start,end);
movies[i] = movie;
}
int index = 0;
int count = 0;
while (true){
int minend = 2000;
for (Movie movie:movies){
if (movie.getStartTime() >= index){
minend = Math.min(minend,movie.getEndTime());
}
}
if (minend == 2000){
break;
} else {
count++;
index = minend;
}
}
System.out.println(count);
n = cin.nextInt();
}
}
static class Movie{
int startTime;
int endTime;
public Movie(int startTime, int endTime) {
this.startTime = startTime;
this.endTime = endTime;
}
public int getStartTime() {
return startTime;
}
public int getEndTime() {
return endTime;
}
}
}
4107:19岁生日礼物-Birthday Gift
import java.util.*;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
int n = cin.nextInt();
for (int i = 0;i < n;i++){
int x = cin.nextInt();
String y = "" + x;
if (x % 19 == 0 || y.contains("19")){
System.out.println("Yes");
} else {
System.out.println("No");
}
}
}
}
2020.1.22
4108:羚羊数量-Number Of Antelope
半夜做这个，脑子不清醒这么简单的一道题绕了半天
import java.util.*;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
//i是第几年，nums[i]表示第i年有多少只
int[] nums = new int[41];
//i是的岁数，ages[i]是这个年龄的的个数
int[] ages = new int[41];
ages[0] = 1;
for (int i = 0;i <= 40;i++){
int sum = 0;
//System.out.println("第"+i+"年-----------------------》");
for (int count:ages){
sum += count;
//System.out.println(count);
}
nums[i] = sum;
int born = 0;
for (int j = 40;j > 0;j--){
ages[j] = ages[j - 1];
}
for (int age = 3;age <= 40;age++){
born += ages[age];
}
ages[0] = born;
}
int n = cin.nextInt();
for (int i = 0;i < n;i++){
int x = cin.nextInt();
//key是羚羊的年龄，value是这个年龄的领养的数量
System.out.println(nums[x]);
}
}
}
4109:公共朋友-Common Friends
import java.util.*;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
int c = cin.nextInt();
for (int i = 0;i < c;i++){
System.out.println("Case "+(i + 1)+":");
int n = cin.nextInt();
int m = cin.nextInt();
int k = cin.nextInt();
Map<Integer,Set<Integer>> friends = new HashMap<>();
for (int j = 1;j <= n;j++){
Set<Integer> friend = new HashSet<>();
friends.put(j,friend);
}
for (int j = 0;j < m;j++){
int f1 = cin.nextInt();
int f2 = cin.nextInt();
friends.get(f1).add(f2);
friends.get(f2).add(f1);
}
for (int j = 0;j < k;j++){
int f1 = cin.nextInt();
int f2 = cin.nextInt();
Set<Integer> friends1 = friends.get(f1);
Set<Integer> friends2 = friends.get(f2);
int count = 0;
if (friends1.size() <= friends2.size()){
for (int friend:friends1){
if (friends2.contains(friend)){
count++;
}
}
} else {
for (int friend:friends2){
if (friends1.contains(friend)){
count++;
}
}
}
System.out.println(count);
}
}
}
}
4110:圣诞老人的礼物-Santa Clau’s Gifts
import java.util.Arrays;
import java.util.Comparator;
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
int n = cin.nextInt();
int weight = cin.nextInt();
Candy[] candies = new Candy[n];
for (int i = 0;i < n;i++){
int v = cin.nextInt();
int w = cin.nextInt();
Candy candy = new Candy(w,v);
candies[i] = candy;
}
Arrays.sort(candies, new Comparator<Candy>() {
@Override
public int compare(Candy o1, Candy o2) {
double price1 = (double)o1.getValue() / o1.getWeight();
double price2 = (double)o2.getValue() / o2.getWeight();
if (price1 > price2){
return -1;
} else if (price1 == price2){
return 0;
} else {
return 1;
}
}
});
float sum = 0;
int index = 0;
while (weight > 0 && index < n){
int min = Math.min(weight,candies[index].getWeight());
float price = (float)candies[index].getValue() / candies[index].getWeight();
sum += min * price;
weight -= min;
index++;
}
System.out.println(sum);
}
static class Candy{
int weight;
int value;
public Candy(int weight, int value) {
this.weight = weight;
this.value = value;
}
public int getWeight() {
return weight;
}
public int getValue() {
return value;
}
}
}
4111:判断游戏胜者-Who Is the Winner
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
int n = cin.nextInt();
for (int i = 0;i < n;i++){
String alice = cin.next();
String bob = cin.next();
compute(alice,bob);
}
}
static void compute(String alice,String bob){
int num1 = oneNum(alice);
int num2 = oneNum(bob);
if (num1 > num2){
System.out.println("Alice");
} else if (num1 < num2){
System.out.println("Bob");
} else {
System.out.println("Tie");
}
}
static String transfer(String str){
int len = str.length();
char[] chars = str.toCharArray();
StringBuilder ans = new StringBuilder("");
for (int i = 2;i < len;i++){
char ch = chars[i];
switch (ch){
case '0':{
ans.append("0000");
break;
}
case '1':{
ans.append("0001");
break;
}
case '2':{
ans.append("0010");
break;
}
case '3':{
ans.append("0011");
break;
}
case '4':{
ans.append("0100");
break;
}
case '5':{
ans.append("0101");
break;
}
case '6':{
ans.append("0110");
break;
}
case '7':{
ans.append("0111");
break;
}
case '8':{
ans.append("1000");
break;
}
case '9':{
ans.append("1001");
break;
}
case 'a':{
ans.append("1010");
break;
}
case 'b':{
ans.append("1011");
break;
}
case 'c':{
ans.append("1100");
break;
}
case 'd':{
ans.append("1101");
break;
}
case 'e':{
ans.append("1110");
break;
}
case 'f':{
ans.append("1111");
break;
}
}
}
return ans.toString();
}
static int oneNum(String str){
String str1 = transfer(str);
char[] chars = str1.toCharArray();
int len = str1.length();
int count = 0;
int left = 0;
while (left < len){
while (left < len && chars[left] == '0'){
left++;
}
if (left < len){
count++;
}
int right = left + 1;
while (right < len && chars[right] == '1'){
right++;
}
left = right;
}
return count;
}
}
4112:情报破译-Cryptanalysis
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
while (cin.hasNext()){
String msg = cin.nextLine();
int count = 0;
char[] chars = msg.toCharArray();
int len = msg.length();
int left = 0;
while (left < len){
count++;
while (left < len && !legal(chars[left])){
System.out.print(chars[left]);
left++;
}
StringBuilder word = new StringBuilder("");
int right = left;
while (right < len && legal(chars[right])){
word.append(chars[right]);
right++;
}
System.out.print(reverse(word.toString(),count));
left = right;
}
System.out.print("\n");
}
}
static String reverse(String string,int i){
StringBuilder ans = new StringBuilder("");
char[] chars = string.toCharArray();
for (char ch:chars){
char ch1;
if (ch >= 'a' && ch <= 'z'){
ch1 = (char)('a' + ((ch - 'a') - i + 26) % 26);
} else {
ch1 = (char)('A' + ((ch - 'A') - i + 26) % 26);
}
ans.append(ch1);
}
ans.reverse();
return ans.toString();
}
static boolean legal(char ch){
return (ch <= 'z' && ch >= 'a') || (ch >= 'A' && ch <= 'Z');
}
}
2020.1.25
大年初一，希望今年平平安安，身体健康，万事如意
4117:简单的整数划分问题
这一题用到dp，new一个二维数组，dp[i][j]其中i表示我们要求的是加起来为i的结果，j表示开头第一个数是j
dp真的是需要积累的
import java.util.Scanner;
public class Main {
private static int[][] dp = new int[51][51];
static void initDp(){
dp[0][0] = 1;
dp[1][1] = 1;
for (int i = 1;i <= 50;i++){
for (int j = 1;j <= i;j++){
int sum = 0;
for (int k = 0;k <= j ;k++){
sum += dp[i - j][k];
}
dp[i][j] = sum;
}
}
}
public static void main(String[] args) {
initDp();
Scanner cin = new Scanner(System.in);
while (cin.hasNext()){
int input = cin.nextInt();
int sum = 0;
for (int i = 1;i <= input;i++){
sum += dp[input][i];
}
System.out.println(sum);
}
}
}
4118:开餐馆
基础dp，用dp[i]表示最后一个选择第i个参观所带来的收益， 我不明白我的程序为什么会超时，我的时间复杂度明明是不会超时的，我感觉是测试用例有问题,这道题把我整放弃了，我还是回去做leetcode了，此博客暂时完结
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
int T = cin.nextInt();
for (int i = 0;i < T;i++){
int n = cin.nextInt();
int distance = cin.nextInt();
int[] dis = new int[n];
int[] value = new int[n];
for (int j = 0;j < n;j++){
dis[j] = cin.nextInt();
}
for (int j = 0;j < n;j++){
value[j] = cin.nextInt();
}
int max = 0;
int[] dp = new int[n];
for (int j = 0;j < n;j++){
int temp = value[j];
int index = 0;
while(dis[j] - dis[index] > distance){
temp = Math.max(temp,value[j] + dp[index]);
index++;
}
dp[j] = temp;
max = Math.max(max,dp[j]);
}
System.out.println(max);
}
}
}
2020.2.18
这瘟疫啥时候能过去。。。
4137:最小新整数：这个问题开始想难了，其实不难
import java.util.Scanner;
import java.util.Stack;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
int t = cin.nextInt();
for (int i = 0;i < t;i++){
String n = cin.next();
int len = n.length();
int k = cin.nextInt();
int count = 0;
Stack<Character> stack = new Stack<>();
char[] chars = n.toCharArray();
for (char ch:chars){
while (!stack.empty() && ch < stack.peek() && count < k){
stack.pop();
count++;
}
stack.push(ch);
}
Stack<Character> temp = new Stack<>();
while (!stack.empty()){
temp.add(stack.pop());
}
StringBuilder stringBuilder = new StringBuilder("");
for (int j = 0;j < len - k;j++){
stringBuilder.append(temp.pop());
}
System.out.println(stringBuilder.toString());
}
}
}
签到题：
4138:质数的和与积
import java.util.*;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
int n = cin.nextInt();
int left = n / 2;
while(left > 1){
int right = n - left;
if (illegal(left) && illegal(right)){
System.out.println(left * right);
break;
}
left--;
}
}
static boolean illegal(int x){
int y = (int)Math.sqrt(x);
for (int i = 2;i <= y;i++){
if (x % i == 0){
return false;
}
}
return true;
}
}
4147:汉诺塔问题(Hanoi)
老经典题了
汉诺塔问题的思路是这样的：
有n个大铁片子要从a借助b到达c，我们记为 F ( n , a , b , c ) F(n,a,b,c) F(n,a,b,c)
事实上，为了完成这个任务，我们必须要经过一个中间状态，那就是将前n-1个铁片放在b上，完了让第n个从a放在c上
那么问题变成这样：
要完成把n个铁片从a借助b到达c，需要分为三步：
- 把n-1个铁片从a借助c放到b上
- 把a上第n个铁片放在c上
- 把b上n-1个铁片借助a放在c上
我们进行抽象：
F ( n , a , b , c ) = F ( n − 1 , a , c , b ) − > 把 n 从 a 放 到 c 上 − > F ( n − 1 , b , a , c ) F(n,a,b,c)=F(n-1,a,c,b)->把n从a放到c上->F(n-1,b,a,c) F(n,a,b,c)=F(n−1,a,c,b)−>把n从a放到c上−>F(n−1,b,a,c)
import java.util.*;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
int n = cin.nextInt();
char a = cin.next().charAt(0);
char b = cin.next().charAt(0);
char c = cin.next().charAt(0);
hanno(n,a,b,c);
}
static void hanno(int n,char a,char b,char c){
if (n == 1){
System.out.println(n + ":" + a + "->" + c);
} else {
hanno(n - 1,a,c,b);
System.out.println(n + ":" + a + "->" + c);
hanno(n - 1,b,a,c);
}
}
}
2020.2.19
做一个简单的一批的题目居然难住了：
836. 矩形重叠
如果连个矩阵 ( x 1 , y 1 , x 2 , y 2 ) , ( x 3 , y 3 , x 4 , y 4 ) (x1,y1,x2,y2),(x3,y3,x4,y4) (x1,y1,x2,y2),(x3,y3,x4,y4)要相交，那么他们俩相交的矩阵就是 ( m a x ( x 1 , x 3 ) , m a x ( y 1 , y 3 ) , m i n ( x 2 , x 4 ) , m i n ( y 2 , y 4 ) ) (max(x1,x3),max(y1,y3),min(x2,x4),min(y2,y4)) (max(x1,x3),max(y1,y3),min(x2,x4),min(y2,y4))
我们只需要判断这个能不能构成举行就可以了
public boolean isRectangleOverlap(int[] rec1, int[] rec2) {
int x5 = Math.max(rec1[0],rec2[0]);
int y5 = Math.max(rec1[1],rec2[1]);
int x6 = Math.min(rec1[2],rec2[2]);
int y6 = Math.min(rec1[3],rec2[3]);
return x5 < x6 && y5 < y6;
}
2020.2.20
4127:迷宫问题
啊这个问题有一点点意思的
BFS+DP
题目要求我们从左上角向右下角去找一条路，但是我们要反过来想，从右下角向左上角去找路，所以我们从右下角开始BFS，记录每个位置到右下角所需的最短路径，最后我们从左上角开始输出就可以了。
import java.util.*;
public class Main {
public static void main(String[] args) {
int[][] matrix = new int[5][5];
int[][] length = new int[5][5];
Scanner cin = new Scanner(System.in);
for (int i = 0;i < 5;i++){
for (int j = 0;j < 5;j++){
matrix[i][j] = cin.nextInt();
length[i][j] = Integer.MAX_VALUE;
}
}
BFS(matrix,length);
print(length,0,0);
}
static void print(int[][] length,int i,int j){
System.out.println("(" + i + ", " + j + ")");
int len = length[i][j];
if (i > 0 && length[i - 1][j] == len - 1) {
print(length, i - 1, j);
}
if (i < 4 && length[i + 1][j] == len - 1){
print(length, i + 1, j);
}
if (j > 0 && length[i][j - 1] == len - 1) {
print(length, i, j - 1);
}
if (j < 4 && length[i][j + 1] == len - 1) {
print(length, i, j + 1);
}
}
static void BFS(int [][] matrix,int[][] length){
int count = 1;
List<Point> points = new ArrayList<>();
points.add(new Point(4,4));
length[4][4] = 0;
while (!points.isEmpty()){
List<Point> points1 = new ArrayList<>();
for (Point point:points){
int x = point.x;
int y = point.y;
if (x > 0 && matrix[x - 1][y] == 0 && length[x - 1][y] == Integer.MAX_VALUE){
length[x - 1][y] = count;
points1.add(new Point(x - 1,y));
}
if (y > 0 && matrix[x][y - 1] == 0 && length[x][y - 1] == Integer.MAX_VALUE){
length[x][y - 1] = count;
points1.add(new Point(x,y - 1));
}
if (x < 4 && matrix[x + 1][y] == 0 && length[x + 1][y] == Integer.MAX_VALUE){
length[x + 1][y] = count;
points1.add(new Point(x + 1,y));
}
if (y < 4 && matrix[x][y + 1] == 0 && length[x][y + 1] == Integer.MAX_VALUE){
length[x][y + 1] = count;
points1.add(new Point(x,y + 1));
}
}
count++;
points = points1;
}
}
static class Point{
private int x;
private int y;
public Point(int x, int y) {
this.x = x;
this.y = y;
}
public int getX() {
return x;
}
public void setX(int x) {
this.x = x;
}
public int getY() {
return y;
}
public void setY(int y) {
this.y = y;
}
}
}
4122:切割回文
import java.util.*;
public class Main {
public static void main(String[] args) {
Scanner cin = new Scanner(System.in);
int T = cin.nextInt();
for (int i = 0;i < T;i++){
String string = cin.next();
char[] chars = string.toCharArray();
int len = string.length();
System.out.println(getCount(chars,0,len - 1));
}
}
static int getCount(char[] chars,int left,int right){
if (left > right){
return -1;
}
int index = left;
while (!islegal(chars,index,right)){
index++;
}
return 1 + getCount(chars, left, index - 1);
}
static boolean islegal(char[] chars,int left,int right){
while (left < right){
if(chars[left] != chars[right]){
return false;
} else {
left++;
right--;
}
}
return true;
}
}
2020.2.22
狗日的瘟疫
leetcode60：第k个排列
public String getPermutation(int n, int k) {
int t = n;
k--;
int[] nums = new int[n];
boolean[] chosen = new boolean[n];
StringBuilder stringBuilder = new StringBuilder("");
for (int i = 1;i <= n;i++){
nums[i - 1] = i;
}
while (t > 0){
t--;
int s = k / fx(t);
int count = 0;
int i = 0;
for (;i < n;i++){
if (!chosen[i]){
count++;
}
if (count > s){
break;
}
}
stringBuilder.append(nums[i]);
chosen[i] = true;
k -= s * fx(t);
}
return stringBuilder.toString();
}
static int fx(int x){
int ans = 1;
for (int i = 2;i <= x;i++){
ans *= i;
}
return ans;
}