(LeetCode) 129. Sum Root to Leaf Numbers

129. 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.

For example,

    1   / \  2   3

The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.

Return the sum = 12 + 13 = 25.

思路

使用分治法，每个节点的和等于左右子树的和，所以可以通过递归的方法来做。

代码

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