Minimum Depth of Binary Tree

来源：Leetcode

原帖：https://oj.leetcode.com/problems/minimum-depth-of-binary-tree/

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.

代码：

 /**  
  * Definition for binary tree  
  * struct TreeNode {  
  *   int val;  
  *   TreeNode *left;  
  *   TreeNode *right;  
  *   TreeNode(int x) : val(x), left(NULL), right(NULL) {}  
  * };  
  */  
 // 16ms  
 class Solution {  
 public:  
   int minDepth(TreeNode *root) {  
     if (!root) return 0;            
     if (!root->left && !root->right) return 1;        
     if (!root->left) return 1 + minDepth(root->right);    
     if (!root->right) return 1 + minDepth(root->left);        
     // root->left && root->right  
     return 1 + min(minDepth(root->left), minDepth(root->right));  
   }  
 };  
   
 // 21ms  
 class Solution {  
 public:  
   int minDepth(TreeNode* root) {  
     if (!root) return 0;  
     int depth = 0;  
     queue<TreeNode*> q;  
     q.push(root);  
     while (!q.empty()) {  
       depth++;  
       int size = q.size();  
       for (int i = 0; i < size; ++i) {  
         TreeNode* node = q.front();  
         q.pop();  
         if (!node->left && !node->right) {  
           return depth; // min depth;  
         }  
         if (node->left) q.push(node->left);  
         if (node->right) q.push(node->right);  
       }  
     }  
   }  
 };