leetcode-111. Minimum Depth of Binary Tree
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平时练习一下leetcode
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先根据牛课网上题练习,同步leetcode官网
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.
思路
- 本题要注意最小深度与最大深度的区别:对于最大深度,不需要考虑当前子树是否为单子树(即一侧树深度为0)的情况,即最大深度一直等于左右子树的最大值;对于最小深度,需要考虑当前子树是否为单子树的情况,对于双子树,其最小深度为左右子树的最小值,对于单子树,其最小深度为左右深度的最大值(因为一侧的子树为0).
Nowcoder
class Solution {
public:
int run(TreeNode *root) { //叶子结点才记录深度,然后不断更新
if(root==nullptr)
return 0;
int l_depth=0,r_depth=0;
l_depth=run(root->left);
r_depth=run(root->right);
if(l_depth==0)
return r_depth+1;
if(r_depth==0)
return l_depth+1;
if(l_depth<r_depth)
return l_depth+1;
else
return r_depth+1;
}
};
leetcode
/**
* 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) return 0;
if(!root->left) return 1 + minDepth(root->right);
if(!root->right) return 1 + minDepth(root->left);
return 1+min(minDepth(root->left),minDepth(root->right));
}
};
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