111. Minimum Depth of Binary Tree

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.

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     int minDepth(TreeNode* root) {
13         if(!root)
14             return 0;
15         if(!root->left)
16             return 1+minDepth(root->right);
17         if(!root->right)
18             return 1+minDepth(root->left);
19         return 1+min(minDepth(root->left),minDepth(root->right));
20     }
21 };

只要有子节点，就算只有一个子节点，当前节点就肯定不是叶节点，需要继续递归