题解 | #二叉树根节点到叶子节点和为指定值的路径#Java91%

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param root TreeNode类 
     * @param sum int整型 
     * @return int整型ArrayList<ArrayList<>>
     */
    ArrayList<ArrayList<Integer>> res;
    public ArrayList<ArrayList<Integer>> pathSum (TreeNode root, int sum) {
        // write code here
        res = new ArrayList<ArrayList<Integer>>();
        if(root == null){
            return res;
        }
        dfs(root,new ArrayList<Integer>(),sum,0);
        return res;
    }
    void dfs(TreeNode root, ArrayList<Integer> set, int sum,int nowsum){
        set.add(root.val);
        nowsum += root.val;
        if(root.left == null && root.right == null){
            if(nowsum == sum)
            res.add(new ArrayList<>(set));
            return;
        }
        if(root.left != null){
            dfs(root.left, set, sum, nowsum);
            set.remove(set.size()-1);
        }
        if (root.right != null){
            dfs(root.right, set, sum, nowsum);
            set.remove(set.size()-1);
        }

    }
}