[LeetCode] 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.

DFS，我们只要叶子节点，和之前的Maximum Depth有点不一样

 1 /**
 2  * Definition for binary tree
 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         // Start typing your C/C++ solution below
14         // DO NOT write int main() function
15         if (root == NULL)
16             return 0;
17             
18         if (root->left == NULL && root->right == NULL)
19             return 1;
20             
21         int leftDepth = minDepth(root->left);
22         int rightDepth = minDepth(root->right);
23         
24         if (leftDepth == 0)
25             return rightDepth + 1;
26         else if (rightDepth == 0)
27             return leftDepth + 1;
28         else
29             return min(leftDepth, rightDepth) + 1;
30     }
31 };