[LeetCode] 129. Sum Root to Leaf Numbers

Sum Root to Leaf Numbers

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.
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.

解析

DFS递归整棵树，当遇到叶子就返回，没往下一层，sum*10.

代码

class Solution {
public:
    int sumNumbers(TreeNode* root) {
        return sumNumbers(root, 0);
    }
    int sumNumbers(TreeNode* root, int sum){
        if(!root)  return 0;
        if(!root->left && !root->right)
            return sum*10 + root->val;
        return sumNumbers(root->left, sum*10+root->val) + sumNumbers(root->right, sum*10+root->val);
    }
};

参考

https://blog.youkuaiyun.com/linhuanmars/article/details/22913699