zac-xin

public class Solution {
    public boolean isValid(String s) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(s == null || s.length() == 0)
            return true;
        
        if(s.length() % 2 == 1)
            return false;
        

zac-xin

public class Solution {
    char symbols[] = {'M', 'D', 'C', 'L', 'X', 'V', 'I'};
    int values[] = {1000, 500, 100, 50, 10, 5, 1};
    
    public int romanToInt(String s) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(s.length() == 0)
            return 0;
            

zac-xin

public class Solution {
    public ArrayList<ArrayList<Integer>> permute(int[] num) {
        // Start typing your Java solution below
        // DO NOT write main() function
        return permuteHelper(num, 0);
    }
    
    public ArrayList<ArrayList<Integer>> permuteHelper(int num[], int index){
        ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
        if(index == num.length - 1){

zac-xin

public class Solution {
    public String addBinary(String a, String b) {
        // Start typing your Java solution below
        // DO NOT write main() function
        int la = a.length();
        int lb = b.length();
        
        int max = Math.max(la, lb);
        
        StringBuilder sum = new StringBuilder("");

zac-xin

public class Solution {
    public ArrayList<String> anagrams(String[] strs) {
        // Start typing your Java solution below
        // DO NOT write main() function
        HashMap<String, ArrayList<String>> map = new HashMap<String, ArrayList<String>>();
        
        ArrayList<String> result = new ArrayList<String>();
        
        if(strs.length < 2)
            return result;

zac-xin

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {

zac-xin

public class Solution {
    public int threeSumClosest(int[] num, int target) {
        // Start typing your Java solution below
        // DO NOT write main() function
        Arrays.sort(num);
        int diff = Integer.MAX_VALUE;
        int closest = Integer.MAX_VALUE;
        
        for(int i =  0; i < num.length - 2; i++){
            int k = i + 1;

zac-xin

import java.util.Stack;

public class Solution {
    public int largestRectangleArea(int[] height) {
        // Start typing your Java solution below
        // DO NOT write main() function
        int i = 0;
        int max = 0;
        Stack<Pair> stack = new Stack<Pair>();
        

zac-xin

public class Solution {
    public ArrayList<String> letterCombinations(String digits) {
        // Start typing your Java solution below
        // DO NOT write main() function
        
        ArrayList<String> result = new ArrayList<String>();
        char str[] = new char[digits.length()];
        
        helper(0, str, result, digits);
        return result;

zac-xin

public class Solution {
    public int sqrt(int x) {
        // Start typing your Java solution below
        // DO NOT write main() function
        long low = 0;
        long high = x;
        while(low <= high){
            long mid = low + (high - low) / 2;
            long result = mid * mid;
            if(result == x){