leetcode 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： 递归求和，第一次发现可以在形参里初始化一个值

class Solution {public:int sumNumbers(TreeNode* r, int b = 0) {if (!r) return 0;if (r->left || r->right) return sumNumbers(r->left, 10 * b + r->val) + sumNumbers(r->right, 10 * b + r->val);else return 10 * b + r->val;}};