Maggie199

    public int trap(int[] A) {
        int count = 0;
        int leftPeak = -1;
        int rightPeak = -1;
        int minPeak = -1;
        boolean flag = false;
        for(int i=0; i<A.length; i++){
            if(isPeak(A,i)){
                leftPeak = rightPeak;
                rightPeak = i;

Maggie199

import java.util.Arrays;
public class Solution {
    public TreeNode buildTree(int[] preorder, int[] inorder) {
        int len = preorder.length;
        if(len == 0){
            return null;
        }
        return buildTreeHelper(preorder, inorder, 0, len-1, 0, len-1);
    }
    public TreeNode buildTreeHelper(int[] preorder, int [] inorder, int ps, int pe, int is, int ie){

Maggie199

import java.util.Arrays;
public class Solution {
    public TreeNode buildTree(int[] inorder, int[] postorder) {
        int in_len = inorder.length;
        int post_len = postorder.length;
        if(post_len == 0)
            return null;
        TreeNode root=new TreeNode(postorder[post_len-1]);
        int position=in_len-1;
        while(inorder[position] != postorder[post_len-1]){

Maggie199

public void rotate(int[][] matrix) {
        int len = matrix.length;
        int start, end, element;
        for(int layer=0; layer<len/2;layer++){
            start = layer;
            end = len-1-start;
            for(int gp=0; gp<end-start;gp++){
                element = matrix[layer][start+gp];
                matrix[layer][start+gp] = matrix[end-gp][layer];
                matrix[end-gp][layer] = matrix[len-1-layer][end-gp];

Maggie199

public int searchInsert(int[] A, int target) {
        for(int i=0;i<A.length;i++){
            if(A[i] == target)
                return i;
            else if(A[i] > target)
                return i;
            else if(i == A.length-1)
                return i+1;
        }
        return -1;

Maggie199

public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> result = new ArrayList<Integer>();
        if(matrix == null || matrix.length == 0)
            return result;
        int endy=matrix.length;
        int endx=matrix[0].length;
        int starty = 0;
        int startx = 0;
        while(startx!=endx && starty!=endy){
            if(starty < endy){

Maggie199

public int threeSumClosest(int[] num, int target) {
        HashSet<Integer> partSum = new HashSet<Integer>();
        partSum.add(num[0]+num[1]);
        int result=num[0]+num[1]+num[2];
        for(int i=2; i<num.length; i++){
            for(int n: partSum){
                if(Math.abs(n+num[i]-target)<Math.abs(result-target)){
                    if(n+num[i] == target)
                        return target;
                    else result = n+num[i];

Maggie199

import java.util.Hashtable;
public class Solution {
    public int[] twoSum(int[] numbers, int target) {
        Hashtable<Integer, Integer> check = new Hashtable<Integer, Integer>();
        for(int i = 0; i<numbers.length;i++){
            if(check.containsKey(target-numbers[i]))
                return new int[]{check.get(target-numbers[i]),i+1};
            else check.put(numbers[i],i+1);
        }
        return null;

Maggie199

import java.util.Hashtable;
public class Solution {
    public int majorityElement(int[] num) {
        Hashtable<Integer,Integer> count = new Hashtable<Integer, Integer>();
        int len = num.length;
        int curr;
        for(int i=0; i<len; i++){
            curr = num[i];
            if(count.containsKey(curr)){
                int temp = count.get(curr);

Maggie199

public List<Integer> getRow(int rowIndex) {
        List<Integer> result = new ArrayList<Integer>();
        for(int i=0; i<=rowIndex; i++){
            if(i == 0 )
                result.add(1);
            else{
                List<Integer> temp = new ArrayList<Integer>(result);
                for(int j=1;j<i;j++){
                    result.set(j, temp.get(j-1) + temp.get(j));
                }