一、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.

Note: A leaf is a node with no children.

Example 1:

Input: root = [3,9,20,null,null,15,7]
Output: 2
Example 2:

Input: root = [2,null,3,null,4,null,5,null,6]
Output: 5

Constraints:

The number of nodes in the tree is in the range [0, 105].
-1000 <= Node.val <= 1000

二、题解

/*** Definition for a binary tree node.* struct TreeNode {*     int val;*     TreeNode *left;*     TreeNode *right;*     TreeNode() : val(0), left(nullptr), right(nullptr) {}*     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}*     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}* };*/
class Solution {
public:int minDepth(TreeNode* root) {int res = 0;queue<TreeNode*> q;if(root != nullptr) q.push(root);while(!q.empty()){int size = q.size();res++;while(size--){TreeNode* t = q.front();q.pop();if(t->left == nullptr && t->right == nullptr) return res;if(t->left != nullptr) q.push(t->left);if(t->right != nullptr) q.push(t->right);}}return res;}
};