LeetCode OJ

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.

解题思路：

1，若树为空返回0

2，若树没有左子树，返回右子树的深度+1

3，若树没有右子树，返回左子树的深度+1

4，否则，返回min(左子树的深度，右子树的深度） + 1

代码：

/**
 * 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) {
        if (root == NULL) return 0;
        
        if (root->left == NULL) return minDepth(root->right) + 1;
        else if (root->right == NULL) return minDepth(root->left) + 1;
        else return min(minDepth(root->left), minDepth(root->right)) + 1;
    }
};