[Leetcode] 113. Path Sum II

Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.

For example:
Given the below binary tree and sum = 22,

              5
             / \
            4   8
           /   / \
          11  13  4
         /  \    / \
        7    2  5   1

return

[
   [5,4,11,2],
   [5,8,4,5]
]

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
import java.util.ArrayList;
public class Solution {
    public ArrayList<ArrayList<Integer>> pathSum(TreeNode root, int sum) {
        ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
        if(root == null) return result;
        ArrayList<Integer> list = new ArrayList<Integer>();
        list.add(root.val);
        findSum(root, sum - root.val, result, list);
        return result;
    }
    private void findSum(TreeNode root, int sum, ArrayList<ArrayList<Integer>> result, ArrayList<Integer> list){
        if(root == null) return;
        if(root.left == null && root.right == null && sum == 0){
             result.add(new ArrayList<Integer>(list));
             return;
        }
        if(root.left != null){
            list.add(root.left.val);
            findSum(root.left, sum - root.left.val, result, list);
            list.remove(list.size() - 1);
        }
        if(root.right != null){
            list.add(root.right.val);
            findSum(root.right, sum - root.right.val, result, list);
            list.remove(list.size() - 1);
        }
    }
}