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。

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int sumNumbers(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if (root == NULL) 
        return 0;
        int sum = 0;
        deque<TreeNode*> layer;
        layer.push_back(root);
        while (!layer.empty()) {
            TreeNode *current = layer.front();
            layer.pop_front();
            if (current->left == NULL && current->right == NULL) {
                sum += current->val;
            }
            if (current->left != NULL) {
                current->left->val += current->val * 10;
                layer.push_back(current->left);
            }
            if (current->right != NULL) {
                current->right->val += current->val * 10;
                layer.push_back(current->right);
            }
        }
        return sum;
    }
};