【leetcode】Minimum Depth of Binary Tree

Question ： 

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.

Anwser 1 ：   

/** * 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 minDepth(TreeNode *root) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        if (root == NULL) return 0;                int left = minDepth(root->left) + 1;        int right = minDepth(root->right) + 1;                // leaf        if (left == 1 || right == 1)            return left > right ? left : right;                    return left < right ? left : right;    }};

Anwser 2 ：    

/** * 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 minDepth(TreeNode *root) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        if (root == NULL) return 0;                int depth = 1;        queue <TreeNode *> current;        queue <TreeNode *> next;        current.push(root);            while (!current.empty())        {            while (!current.empty())            {                TreeNode *n = current.front();                current.pop();                if (n->left==NULL && n->right == NULL) return depth;                if (n->left) next.push(n->left);                if (n->right) next.push(n->right);            }                        queue <TreeNode *> t;   // init queue            current = next;            next = t;            depth += 1;        }        return depth;    }};