leetcode:Minimum Depth of Binary Tree

题目描述：

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.（从根节点到叶节点经过的最短路径经过的节点数）

实现：

1.递归

class Solution {public:    int run(TreeNode *root) {        if(root==NULL)            return 0;        int depthl=run(root->left);        int depthr=run(root->right);                 if(depthl==0&&depthr==0)            return 1;        if(depthl==0)            depthl=INT_MAX;//没有左节点一定不是该路径        if(depthr==0)            depthr=INT_MAX;        return min(depthl,depthr)+1;    }};

2.非递归

按广度优先遍历（按层次遍历），若某一层出现了叶节点就返回其深度。

int run(TreeNode *root) {    queue<pair<TreeNode*, int>> q;    if(root == NULL) return 0;    q.push(make_pair(root,1));    while(!q.empty()){        pair<TreeNode*, int> cur = q.front();        q.pop();        if(!cur.first->left && !cur.first->right) return cur.second;        if(cur.first->left)            q.push(make_pair(cur.first->left,cur.second+1));        if(cur.first->right)            q.push(make_pair(cur.first->right,cur.second+1));    }}

其中用到了STL容器类。