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/*
* @lc app=leetcode.cn id=111 lang=cpp
*
* [111] 二叉树的最小深度
*
* https://leetcode-cn.com/problems/minimum-depth-of-binary-tree/description/
*
* algorithms
* Easy (36.51%)
* Total Accepted: 10.5K
* Total Submissions: 28.6K
* Testcase Example: '[3,9,20,null,null,15,7]'
*
* 给定一个二叉树,找出其最小深度。
*
* 最小深度是从根节点到最近叶子节点的最短路径上的节点数量。
*
* 说明: 叶子节点是指没有子节点的节点。
*
* 示例:
*
* 给定二叉树 [3,9,20,null,null,15,7],
*
* ⁠ 3
* ⁠ / \
* ⁠ 9 20
* ⁠ / \
* ⁠ 15 7
*
* 返回它的最小深度  2.
*
*/
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
//dfs.递归。E
class Solution {
public:
int minDepth(TreeNode* root) {
//root==nullptr,0
if(!root)
return 0;
//left==nullptr->f(right)+1
if(!root->left) return 1+minDepth(root->right);
//right==nullptr->f(left)+1
if(!root->right) return 1+minDepth(root->left);
//none of above==nullptr->min(f(left),f(right))+1
return 1+min(minDepth(root->left),minDepth(root->right));
}
};
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