题目链接：二叉树中和为某一值的路径

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 {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @param target int整型 
     * @return int整型ArrayList<ArrayList<>>
     */
    ArrayList<ArrayList<Integer>> res = new ArrayList<>();
    ArrayList<Integer> path = new ArrayList<>();
    public ArrayList<ArrayList<Integer>> FindPath (TreeNode root, int sum) {
        if(root == null) return res;
        dfs(root, sum);
        return res;
    }

    public void dfs(TreeNode root, int sum){
        if(root == null) return ;
        path.add(root.val);
        sum -= root.val;
        if(root.left == null && root.right == null && sum == 0) res.add(new ArrayList<>(path));
        dfs(root.left, sum);
        dfs(root.right, sum);
        path.remove(path.size() - 1);
    }
}