[LeetCode] 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]
]

[Solution].java

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ArrayList<ArrayList<Integer>> pathSum(TreeNode root, int sum) {
        // Start typing your Java solution below
        // DO NOT write main() function
        ArrayList<ArrayList<Integer>> all = new ArrayList<ArrayList<Integer>>();
        ArrayList<Integer> one = new ArrayList<Integer>();
        hasPathSum(sum, root, one, all);
        return all;
    }
 
    private void hasPathSum(int last, TreeNode root, ArrayList<Integer> one,
            ArrayList<ArrayList<Integer>> all){
        if(root == null) return;

        one.add(root.val);
        int now = last - root.val;
 
        if(root.left == null && root.right == null){
            if(now == 0) all.add(new ArrayList<Integer>(one));
        }
        else{
            hasPathSum(now, root.left, one, all);
            hasPathSum(now, root.right, one, all);
        }
        one.remove(one.size() - 1);
    }
}