【Minimum Depth of Binary Tree】cpp

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) {if (!root) return 0;if ( !root->left && !root->right) return 1;if ( root->left && root->right ) return std::min( Solution::minDepth(root->left)+1, Solution::minDepth(root->right)+1);if ( root->left ) return Solution::minDepth(root->left)+1;if (root->right ) return Solution::minDepth(root->right)+1;}
};

tips：

深搜思路（递归实现）。这里需要控制向下进行的条件。

1. 如果root是NULL，返回0

2. 如果root不是NULL，且left和right都是NULL，则到达叶子节点返回1（代表算上叶子节点的那一层）

3. 如果root->left和root->right都不为NULL，则继续往两边深搜

4. 如果root不是NULL，但root->left或root->right哪一方为NULL，则为NULL的一端不会再有叶子节点出现，不能再往下走了。

完毕。

============================================

第二次过这道题，上来没有把终止条件想完全。终止条件应该是达到叶子简单root->left root->right都为空。

修改了一次后AC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 ) return 0;int min_depth = INT_MAX;Solution::depth(root, min_depth, 1);return min_depth;}static void depth(TreeNode* root, int& min_depth, int dep){if ( !root->left && !root->right ) min_depth = min(min_depth,dep);            if ( root->left ) Solution::depth(root->left, min_depth, dep+1);if ( root->right ) Solution::depth(root->right, min_depth, dep+1);}
};

转载于:https://www.cnblogs.com/xbf9xbf/p/4508762.html

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