题解 | #二叉树根节点到叶子节点的所有路径和# 递归

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 {
    int sum = 0;
    public void reachLeaf(TreeNode root, int num) {
        if (root == null) {
            return;
        } else if (root.left == null && root.right == null) {
            int t = num  + root.val;
            sum += t;
            reachLeaf(root.left, t * 10);
            reachLeaf(root.right, t * 10);
        } else {
            int t = num  + root.val;
           // sum += t;
            reachLeaf(root.left, t * 10);
            reachLeaf(root.right, t * 10);
        }


    }
    public int sumNumbers (TreeNode root) {
        reachLeaf(root, 0);
        return sum;
    }
}

节点的值，每下一层，等于上一层计算的值 * 10 + 叶子节点的值，区别处理叶子节点和非叶节点即可。