LeetCode刷题笔记--111. Minimum Depth of Binary Tree

111. Minimum Depth of Binary Tree

Easy

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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.

Note: A leaf is a node with no children.

Example:

Given binary tree [3,9,20,null,null,15,7],

    3
   / \
  9  20
    /  \
   15   7

return its minimum depth = 2.

刷了100后，紧接着刷了这道。特别要注意当left或者right某一边是NULL的时候，返回一个很大的值。不写这一句会报错，报错的case：[1,2]

下面是AC的代码：

/**
 * 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 look(TreeNode* root, int dist)
    {
        if(root!=NULL)
        {
            dist++;
            if(root->left==NULL&&root->right==NULL)
            {
                return dist;
            }
            return min(look(root->left,dist),look(root->right,dist));
        }
        else return 0x7fffffff;
        
    }
    
    int minDepth(TreeNode* root) {
        if(root==NULL)return 0;
        int distance=1;
        if(root->left==NULL&&root->right==NULL)return 1;
        return min(look(root->left,1),look(root->right,1));
    }
};