b27lu

#define a class to represent the x and y coordinates of points
class Point:
    def __init__(self,x,y):
        self.x = x
        self.y = y
        
#judges if point A,B,C are counter-clockwise
def ccw(A,B,C):
	return (C.y-A.y)*(B.x-A.x) > (B.y-A.y)*(C.x-A.x)

b27lu

public class Solution {
    public ArrayList<ArrayList<Integer>> subsets(int[] S) {
        if(S == null)
            return null;
            
        ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
        //empty set is the subset of any set
        result.add(new ArrayList<Integer>());
        
        //sort array to statisfy the requirement of non-descending order

b27lu

public class Solution {
    public ArrayList<ArrayList<Integer>> subsetsWithDup(int[] num) {
        if(num == null)
            return null;
        
        ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
        ArrayList<Integer> temp = new ArrayList<Integer>();
        
        result.add(temp);
        

b27lu

/*
 *Key point: dfs, 
 *  it's similar to question Subsets; however, we need all elements rather than subsets
 *  so, we have to scan from beginning of array and need a boolean array to store which element has been visited
 */

public class Solution {
    public ArrayList<ArrayList<Integer>> permute(int[] num) {
        if(num == null)
            return null;

b27lu

public class Solution {
    public ArrayList<ArrayList<Integer>> combinationSum(int[] candidates, int target) {
        if(candidates == null)
            return null;
            
        ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
        ArrayList<Integer> temp = new ArrayList<Integer>();
        if(target <= 0)
            return result;
        

b27lu

public class Solution {
    public ArrayList<ArrayList<Integer>> combine(int n, int k) {
        ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
        if(n <= 0 || k<=0)
            return result;
        ArrayList<Integer> temp = new ArrayList<Integer>();
        
        dfsWorker(n, k, result, temp, 1);
        return result;
    }

b27lu

public class Solution {
    public ArrayList<String> generateParenthesis(int n) {
        ArrayList<String> result = new ArrayList<String>();
        StringBuilder sb = new StringBuilder();
        
        if(n <= 0)
            return result;
            
        dfsWorker(n, result, sb, 0, 0);
        return result;

b27lu

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

b27lu

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

b27lu

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