算法进阶指南-基础算法-贪心
1.Sunscreen
题目链接
代码:
import java.util.Arrays;
import java.util.Comparator;
import java.util.Scanner;
import java.util.HashMap;
public class Main {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
int C = in.nextInt();
int L = in.nextInt();
int[] minSPF = new int[C];
int[] maxSPF = new int[C];
int[] SPF = new int[L];
int[] cover = new int[L];
for(int i=0;i<C;i++){
minSPF[i]=in.nextInt();
maxSPF[i]=in.nextInt();
}
for(int i=0;i<L;i++){
SPF[i]=in.nextInt();
cover[i]=in.nextInt();
}
Integer[] c = new Integer[C];
for(int i=0;i<C;i++)c[i]=i;
Arrays.sort(c, new Comparator<Integer>() {
@Override
public int compare(Integer o1, Integer o2) {
return minSPF[o2]-minSPF[o1];
}
});
int res = 0;
for(int i=0;i<C;i++){
int ix = c[i];
int minSPFi = minSPF[ix];
int maxSPFi = maxSPF[ix];
int maxIx = 0;
int maxSPFC = Integer.MIN_VALUE;
boolean findOne = false;
for(int j=0;j<L;j++){
if(SPF[j]>=minSPFi&&SPF[j]<=maxSPFi){
//需要满足条件
//System.out.println("im in!");
if(SPF[j]>maxSPFC&&cover[j]>0){
maxSPFC=SPF[j];
maxIx = j;
findOne=true;
//System.out.println(maxIx);
}
}
}
/*
贪心策略：由于minSPF按照递减策略排序，那么每一个不低于当前minSPF的防晒霜都不会低于其他后续防晒霜的minSPF，
对于当前可选的x，y，如果SPF[y]>SFP[x],那么后续奶牛只可能有三种情况“x,y都可”，“x可，y大于maxSPF了”，“x，y都不可”
选择SPF最大的显然能够满足更多奶牛们的要求
*/
if(findOne){
cover[maxIx]--;//用掉一瓶
res++;//满足一头牛
}
}
System.out.println(res);
}
}
2.Stall Reservations
题目链接
import java.util.Arrays;
import java.util.Comparator;
import java.util.Scanner;
public class Main
{
public static void main(String[] args) {
Scanner sc=new Scanner(System.in);
int n;
n=sc.nextInt();
row x[]=new row[50000+10];
int room[]=new int[50000+10];
for(int i=1;i<=n;i++)
{
x[i]=new row();
x[i].begin=sc.nextInt();
x[i].end=sc.nextInt();
x[i].z=i;
}
Arrays.sort(x,1,n+1);
int ans=1;
for(int i=1;i<=n;i++)
{
int biao=0;
int min=999999;
for(int j=1;j<=ans;j++)
{
if(room[j]<x[i].begin&&room[j]<min)
{
biao=j;
min=room[j];
}
}
if(biao==0){
ans++;
room[ans]=x[i].end;
x[i].ans=ans;
}
else
{
room[biao]=x[i].end;
x[i].ans=biao;
}
}
Arrays.sort(x, 1, n + 1, new Comparator<row>() {
@Override
public int compare(row o1, row o2) {
return o1.z-o2.z;
}
});
System.out.println(ans);
for(int i=1;i<=n;i++)
System.out.println(x[i].ans);
}
}
class row implements Comparable<row>{
int begin,end;
int ans;
int z;
@Override
public int compareTo(row o) {
return begin-o.begin;
}
}
3.Radar Installation
题目链接
代码:
import java.util.Arrays;
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int n = sc.nextInt();
int d = sc.nextInt();
C[] node = new C[n];
boolean f = true;
int x,y;
for(int i=0;i<n;i++) {
x = sc.nextInt();
y = sc.nextInt();
if(y>d) {
f = false;
break;
}
double len = Math.sqrt(d*d-y*y);
node[i] = new C(x-len,x+len);
}
if(!f) {
System.out.println(-1);
}else {
Arrays.sort(node);
int ans = 0;
double r = -1e10;
for(int i=0;i<n;i++) {
if(node[i].l>r+1e-6) {
ans++;
r = node[i].r;
}
}
System.out.println(ans);
}
}
}
class C implements Comparable<C>{
double l,r;
public C(double l,double r) {
this.l = l;
this.r = r;
}
public int compareTo(C o) {
if(this.r>o.r)
return 1;
else
return -1;
}
}
4.国王的游戏
题目链接
代码:
import java.math.BigInteger;
import java.util.Arrays;
import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
// @author:jahup
public class Main {
public static void main( String args[] ){
Scanner sc=new Scanner(System.in);
int n;
final int N=10000+10;
n=sc.nextInt();
human all[]=new human[N];
for(int i=1;i<=n+1;i++){
all[i]=new human(sc.nextInt(),sc.nextInt());
}
Arrays.sort(all,2,n+2);
BigInteger all_=new BigInteger("1");
BigInteger max=new BigInteger("0");
for(int i=1;i<=n+1;i++){
BigInteger now_x=new BigInteger(all[i].x.toString());
BigInteger now_y=new BigInteger(all[i].y.toString());
max=all_.divide(now_y).compareTo(max)>0?all_.divide(now_y):max;
all_=all_.multiply(now_x);
}
System.out.println(max.toString());
}
}
class human implements Comparable<human>{
Integer x,y;
public human(int x, int y) {
this.x = x;
this.y = y;
}
@Override
public int compareTo(human o) {
return x*y-o.x*o.y;
}
}
5.Color a Tree
题目链接
代码:
import java.util.Scanner;
public class Main {
static int n,root;
static E[] node = new E[1005];
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
n = sc.nextInt();
root = sc.nextInt();
int res = 0;
for(int i=1;i<=n;i++) {
int a = sc.nextInt();
node[i] = new E(i,a,1,a);
res += a; //每个都先是独立的点
}
for(int i=1;i<n;i++) {
int a = sc.nextInt();
int b = sc.nextInt();
node[b].father = a;
}
for(int i=1;i<n;i++) {
int p = find(); //找到均值最大的点
int f = node[p].father;
res += node[p].sum*node[f].size; //与父节点合并 添加在后面
node[p].avg = -1; //与父节点已经合并 删出该点
for(int j=1;j<=n;j++) {
//在把该节点的子节点与新父节点连接
if(node[j].father == p) {
node[j].father = f;
}
}
//更新父节点
node[f].sum += node[p].sum;
node[f].size += node[p].size;
node[f].avg = node[f].sum*1.0/node[f].size;
}
System.out.println(res);
}
public static int find() {
int t = 0;
double avg = 0;
for(int i=1;i<=n;i++) {
if(i!=node[i].father&&avg<node[i].avg) {
avg = node[i].avg;
t = i;
}
}
return t;
}
}
class E{
int father,sum,size;
double avg;
public E(int father,int sum,int size,double avg) {
this.father = father;
this.sum = sum;
this.size = size;
this.avg = avg;
}
}