- 学生会主席考前po答案， 你怎么想的，该怎么办.
- 如何找一个跟你不同的人的共同点.
- 你上课一个做的project 队友要走 你该怎么办
- 你的专业怎么选的，你现在如何看
- First Unique Character in a String
class Solution {
public int firstUniqChar(String s) {
int[] letters = new int[26];
for(int i=0; i- Climbing Stairs
class Solution {
public int climbStairs(int n) {
if(n==1) return 1;
if(n==2) return 2;
int pre1 = 1;
int pre2 = 2;
int res = 0;
for(int i=2; i- Valid Anagram
class Solution {
public boolean isAnagram(String s, String t) {
if(s==null||t==null||s.length()!=t.length()) return false;
int[] fre = new int[26];
char[] ss = s.toCharArray();
char[] tt = t.toCharArray();
for(int i=0; i
如果包含其他字符和空格
class Solution {
public static boolean isAnagram(String s, String t) {
// to lower case
s = s.toLowerCase();
t = t.toLowerCase();
// to char array
char[] ss = s.toCharArray();
char[] tt = t.toCharArray();
// fre array
int[] fre = new int[256];
for(char c : ss){
if(c>='1'&&c<='9'||c>='a'&&c<='z'){
fre[c]++;
}
}
for(char c : tt){
if(c>='1'&&c<='9'||c>='a'&&c<='z'){
fre[c]--;
}
}
for(int i : fre){
if(i!=0) return false;
}
return true;
}
public static void main(String[] args) {
System.out.println(isAnagram("s.,%%0t$s#t@", "0 tt@!ss#"));
System.out.println(isAnagram("sa", "ss"));
}
}
class Solution {
// time: 2n space: n
public static int countPairs(int k, int[] pairs) {
if(pairs==null) return 0;
// element, frequence
Map map = new HashMap<>();
int count = 0;
for(int i : pairs) {
map.put(i, map.getOrDefault(i, 0)+1);
}
for(int i : pairs){
if(map.get(k-i)!=null) count+=map.get(k-i);
// if i + i = k
if(k%2==0 && i==k/2) count--;
}
return count / 2;
}
public static void main(String[] args) {
int[] pairs = new int[] {2, 2, 5, 7, 3, 3, 1, 1};
System.out.print(countPairs(4, pairs));
int[] pairs2 = new int[] {};
System.out.print(countPairs(5, pairs2));
int[] pairs3 = null;
System.out.print(countPairs(5, pairs3));
}
}
找数组中第二小的元素
class Solution {
// time: n space: 1
public static int secLargest(int[] nums) {
int first=Integer.MIN_VALUE;
int second=Integer.MIN_VALUE;
for(int i : nums) {
if(i>first){
second = first;
first = i;
}
else if(i>second && i!=first) second = i;
}
if(second==Integer.MIN_VALUE) return 0; // no second largest
return second;
}
public static void main(String[] args) {
int[] nums = new int[] {2, 2, 5, 7, 3, 3, 1, 1};
System.out.print(secLargest(pairs));
}
}
给两个数组求点乘（dot product）
class Solution {
// time: n space: 1
public static int dotProduct(int[] nums1, int[] nums2) {
int sum = 0;
if(nums1==null||nums2==null||nums1.length!=nums2.length) return sum;
for(int i=0; i- Reverse String
class Solution {
public String reverseString(String s) {
char[] ss = s.toCharArray();
int p = 0;
int q = ss.length-1;
while(p给一个字符串s，找出所有Unique的长度为k的substring，并排序。
比如caaab，k = 2，返回 aa, ab, ca. 不重复子串.
输入是一个string和一个substr长度，返回String[]所有unique substrs.
public class tyr {
public static String[] subString(String s, int k) {
if(s==null||s.length() set = new TreeSet<>();
for(int i=0; i<=s.length()-k;i++) {
set.add(s.substring(i, i+k));
}
String[] res = new String[set.size()];
int i=0;
for (String string : set) {
res[i]=string;
i++;
}
return res;
}
public static void main(String[] args) {
String[] ss = subString("sabb", 3);
for (String s : ss) {
System.out.println(s);
}
}
}
给一个数组，每一项是学生名字和分数，学生名字可能有重复，找出所有考试平均分最高的分数。比如 [['bob', '88'], ['ted', '100'], ['ted', '20']]，返回88
第二题一开始有个case没过，有点tricky，因为分数可能有负数，然后负数需要取floor，所以不能直接用int作除法，要double做除法，然后取floor以后再转成Int. 比如 -123 / 10 = -12，但应该要-13
- Best Average Grade：input是String[][]，两列，第一列是名字，第二列是分数。要计算每一个人的平均分数，返回最高的分数。注意要用double。
public class tyr {
public static int bestAverageGrade(String[][] s) {
Map map = new HashMap<>();
// fre, total points
for (String[] row : s) {
if (map.containsKey(row[0])) {
int[] grad = map.get(row[0]);
grad[0] += 1;
grad[1] += Integer.parseInt(row[1]);
map.put(row[0], grad);
} else {
map.put(row[0], new int[]{1, Integer.parseInt(row[1])});
}
}
int max = Integer.MIN_VALUE;
for (int[] ave : map.values()) {
int total = ave[1];
int fre = ave[0];
if(total>=0) max = Math.max(total/fre, max);
else {
Double res = (double)total/fre;
max = Math.max((int)Math.floor(res), max);
}
}
return max;
}
public static void main(String[] args) {
String[][] ss = new String[][]{{"tod", "0"},{"tod", "0"},{"tod", "0"},
{"tod", "0"},{"tod", "0"},{"tod", "0"},{"tod", "0"},{"tod",
"0"},
{"tod", "-3"},
{"tod",
"-120"}, {"anny",
"-88888"}};
System.out.println(bestAverageGrade(ss));
}
}
Compress String(run length encoding): input: aaabbbccccc output: a3b3c5
class Solution {
public int compress(char[] chars) {
int anchor = 0, write = 0;
for (int read = 0; read < chars.length; read++) {
if (read + 1 == chars.length || chars[read + 1] != chars[read]) {
chars[write] = chars[anchor];
write++;
if (read > anchor) {
for (char c: ("" + (read - anchor + 1)).toCharArray()) {
chars[write] = c;
write++;
}
}
anchor = read + 1;
}
}
return write;
}
}