二叉树中和为某一值的路径

import java.util.ArrayList;
import java.util.*;
/**
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
public class Solution {
    public ArrayList<ArrayList<Integer>> FindPath(TreeNode root,int target) {
        ArrayList<ArrayList<Integer>> ans = new ArrayList<ArrayList<Integer>>();
        if(root == null) return ans;
        Stack<Integer> stack = new Stack<Integer>();
        func(ans, stack, root, 0, target);
        return ans;
    }

    private void func(ArrayList<ArrayList<Integer>> ans, Stack<Integer> stack, TreeNode root, int sum, int target){
        sum += root.val;
        stack.push(root.val);
        if(root.left == null && root.right == null){
            if(sum == target){
                ans.add(new ArrayList<Integer>(stack));
            }
        }

        if(root.left != null){
            func(ans, stack, root.left, sum, target);
        }

        if(root.right != null){
            func(ans, stack, root.right, sum, target);
        }
        stack.pop();
    }
}