BiruLyu

public class Solution {
    public int[] twoSum(int[] nums, int target) {
        
        HashMap<Integer,Integer> bufferMap = new HashMap<Integer,Integer>();
        int[] res = new int[2];
        
        for(int i = 0; i< nums.length; i++){
            if(bufferMap.containsKey(nums[i])){
                res[0] = bufferMap.get(nums[i]);
                res[1] = i;

BiruLyu

public class NumArray {
    
    private int[] nums;
    private int[] BITree;
    
    public NumArray(int[] nums) {
        int len = nums.length;
        this.nums = nums;
        this.BITree = new int[len + 1];
        for( int i = 0; i < len; i++){

BiruLyu

public class NumMatrix {
    private int[][] nums;
    private int[][] BITree;
    private int m;
    private int n;
    
    public NumMatrix(int[][] matrix) {
        
        //if (matrix==null||matrix.length == 0 || matrix[0].length == 0) return;//["NumMatrix"] [[[]]]
         if (matrix==null||matrix.length == 0) return;

BiruLyu

public class Solution {
    public int removeElement(int[] nums, int val) {
        int i = 0;
        for(int j = 0; j < nums.length;j++){
            if(nums[j]!=val){
                nums[i]=nums[j];
                i ++;
            }
        }
        return i;

BiruLyu

class Solution {
    public double findMedianSortedArrays(int[] nums1, int[] nums2) {
        if (nums1 == null && nums2 == null) return 0.0;
        int len1 = nums1.length, len2 = nums2.length;
        int left = (len1 + len2) / 2;
        int right = (len1 + len2) / 2 + 1;
        if ((len1 + len2) % 2 != 0) {
            return (double)findKth(nums1, 0, nums2, 0, right);
        } else {
            return (findKth(nums1, 0, nums2, 0, left) + findKth(nums1, 0, nums2, 0, right)) / 2.0; 

BiruLyu

public class Solution {
    public List<String> findRepeatedDnaSequences(String s) {
        List<String> res = new LinkedList<String>();
        Set<String> explored = new HashSet<String>();
        Set<String> repeat = new HashSet<String>();//avoid repetition in res 
        
        for( int i = 0; i < s.length() - 9; i++){
            String temp = s.substring(i,i + 10);
            if(!explored.add(temp) && repeat.add(temp)){
                res.add(temp);

BiruLyu

public class TwoSum {
        Set<Integer> sum;
        Set<Integer> num;
        
        TwoSum(){
            sum = new HashSet<Integer>();
            num = new HashSet<Integer>();
        }
        // Add the number to an internal data structure.
    	public void add(int number) {

BiruLyu

class Solution {
    public int lengthOfLongestSubstringTwoDistinct(String s) {
        if (s == null || s.length() < 1) return 0;
        int count = 0, end = 0, start = 0, res = 0;
        int[] vector = new int[256];
        char[] str = s.toCharArray();
        while (end < str.length) {
            if (vector[str[end++]]++ == 0) count++;
            while (count > 2) {
                if (--vector[str[start++]] == 0) count--;

BiruLyu

/**
 * Definition for a point.
 * class Point {
 *     int x;
 *     int y;
 *     Point() { x = 0; y = 0; }
 *     Point(int a, int b) { x = a; y = b; }
 * }
 */
class Solution {

BiruLyu

public class Solution {
    
    public String countChar(String str){
        int[] vector = new int[26];
        for(char c : str.toCharArray()){
            vector[c - 'a']++;
        }
        return Arrays.toString(vector);
    }
    public List<List<String>> groupAnagrams(String[] strs) {