LeetCode -- Minimum Depth of Binary Tree

题目描述：

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.

就是求一个树的最小层数。

思路：
从根节点进行BFS ，找到第一个叶子节点即可。

实现代码：

/**
* Definition for a binary tree node.
* public class TreeNode {
*     public int val;
*     public TreeNode left;
*     public TreeNode right;
*     public TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public int MinDepth(TreeNode root)
{
if(root == null){
return 0;
}

var layer = 1;
var nodes = new List<TreeNode>();
LoadChildren(ref nodes, root);
if(nodes.Count == 0){
return layer;
}

layer ++;

MinDepth(nodes,ref layer);
return layer;
}
private void MinDepth(List<TreeNode> parents, ref int layer){
var next = new List<TreeNode>();
for(var i = 0;i < parents.Count; i++){
if(parents[i].left == null && parents[i].right == null){
return;
}
if(parents[i].left != null){
next.Add(parents[i].left);
}
if(parents[i].right != null){
next.Add(parents[i].right);
}
}

layer ++;
MinDepth(next,ref layer);
}
private void LoadChildren(ref List<TreeNode> nodes, TreeNode node){
if(node.left != null){
nodes.Add(node.left);
}
if(node.right != null){
nodes.Add(node.right);
}
}
}