[leetcode]Minimum Depth of Binary Tree--二叉树层序遍历的应用

题目：

Given a binary tree, find its minimum depth.

The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.

分析：
要得出二叉树中全部从根到叶子节点路径中，经过结点最少路径上的节点数。

採用二叉树的层序遍历思想。每遍历一层。高度加一，仅仅要遇到叶子节点，就终止，并返回当前层数。
代码：

class Solution {
public:
    int minDepth(TreeNode* root) {
        deque<TreeNode*> store;

        int left_num;
        int res = 0;
        if(!root)
            return res;
        store.push_back(root);
        while(!store.empty()) {
            res++;
            vector<int> res_t;
            left_num = store.size(); 
            while(left_num-- > 0) {
                const TreeNode* tmp = store.front();
                if(!tmp->left&&!tmp->right)
                    return res;
                store.pop_front();
                res_t.push_back(tmp->val);
                if(tmp->left)
                    store.push_back(tmp->left);
                if(tmp->right)
                    store.push_back(tmp->right);
            }
        }

    }
};