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.
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求二叉树的最小深度，嗯，这个题可以用DFS，也可以用BFS，我这个题先用BFS写。
C++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) { queue<TreeNode*> q; if(!root) return 0; q.push(root); int sum = 0; while(!q.empty()){ sum++; for(int i = q.size(); i > 0; i--){ //必须写循环，如果不写，对于[1,2,3,4,5]，将会返回3，与题目要求不符。 auto t = q.front(); q.pop(); if(!t->left &&!t->right) return sum; if(t->left) q.push(t->left); if(t->right) q.push(t->right); } } return 0; } };
(二叉树 BFS) leetcode 111. Minimum Depth of Binary Tree
原文：https://www.cnblogs.com/Weixu-Liu/p/10714886.html