LeetCode-Sum Root to Leaf Numbers

基本可以算是树的层级遍历，很简单，一次就过了小数据和大数据；因为返回的是int，所以也不用考虑溢出的问题，直接逐层更新节点的数值，遇到叶子节点则加入到sum中，遍历结束之后返回sum即可。

 1 /**
 2  * Definition for binary tree
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     int sumNumbers(TreeNode *root) {
13         // Start typing your C/C++ solution below
14         // DO NOT write int main() function
15         if (root == NULL) 
16         return 0;
17         int sum = 0;
18         deque<TreeNode*> layer;
19         layer.push_back(root);
20         while (!layer.empty()) {
21             TreeNode *current = layer.front();
22             layer.pop_front();
23             if (current->left == NULL && current->right == NULL) {
24                 sum += current->val;
25             }
26             if (current->left != NULL) {
27                 current->left->val += current->val * 10;
28                 layer.push_back(current->left);
29             }
30             if (current->right != NULL) {
31                 current->right->val += current->val * 10;
32                 layer.push_back(current->right);
33             }
34         }
35         return sum;
36     }
37 };