leetcode [129]Sum Root to Leaf Numbers

佚名 6年前 (2019-04-16) 随笔 1039人围观抢沙发百度已收录

Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.

An example is the root-to-leaf path 1->2->3 which represents the number 123.

SRE实战互联网时代守护先锋，助力企业售后服务体系运筹帷幄！一键直达领取阿里云限量特价优惠。

Find the total sum of all root-to-leaf numbers.

Note: A leaf is a node with no children.

Example:

Input: [1,2,3]
    1
   / \
  2   3
Output: 25
Explanation:
The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.
Therefore, sum = 12 + 13 = 25.

Example 2:

Input: [4,9,0,5,1]
    4
   / \
  9   0
 / \
5   1
Output: 1026
Explanation:
The root-to-leaf path 4->9->5 represents the number 495.
The root-to-leaf path 4->9->1 represents the number 491.
The root-to-leaf path 4->0 represents the number 40.
Therefore, sum = 495 + 491 + 40 = 1026.

题目大意：

求解从根节点到叶节点的生成数的总和。

解法：

采用深度优先遍历算法。

java:

class Solution {
    int res;

    void dfs(TreeNode node,int tmpSum){
        if(node==null) return;
        if(node.left==null&&node.right==null){
            res+=tmpSum;
            return;
        }
        if(node.left!=null) dfs(node.left,tmpSum*10+node.left.val);
        if(node.right!=null) dfs(node.right,tmpSum*10+node.right.val);
    }
    
    public int sumNumbers(TreeNode root) {
        if(root==null) return 0;
        int tmpSum=root.val;
        res=0;
        dfs(root,tmpSum);
        return res;
    }
}