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.

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刚开始写的代码是这样的。

        if(root==NULL) return 0;
        return min(mindeep(root->right)+1,mindeep(root->left)+1);

看出问题了吧，这段代码“看上去”是正确的，但是对于这种结构

              1
             / 
            2 

              5
             / 
            4   8
           /     
          11      4
对于以上两种结构都是计算错误，因为第一种结构它把根节点自己也看做一条路径，这样是不对的。
所以要做判断，当根节点只有一条路径的时候，只计算一条路径的长度，而不是继续选最小了。

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

};