LeetCode minDepth of 2 bin tree

111. 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 a binary tree node.
* 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
return minRec(root);
}

int minRec( TreeNode * root) {
if(!root) return 0;

if(root->left == NULL && root->right == NULL) return 1;

int leftDepth = minRec(root->left);
int rightDepth = minRec(root->right);
if(root->left == NULL)  return 1 + rightDepth;
else if(root->right == NULL) return 1 + leftDepth;
else return min(leftDepth,rightDepth) + 1;

}
};