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节点的最短路径的节点数量。
详见：https://leetcode.com/problems/minimum-depth-of-binary-tree/description/
Java实现：
递归实现：
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public int minDepth(TreeNode root) {
if(root==null){
return 0;
}
int minLeft=minDepth(root.left);
int minRight=minDepth(root.right);
if(minLeft==0||minRight==0){
return minLeft>=minRight?minLeft+1:minRight+1;
}
return Math.min(minLeft,minRight)+1;
}
}
非递归实现：
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public int minDepth(TreeNode root) {
if(root==null){
return 0;
}
LinkedList<TreeNode> que=new LinkedList<TreeNode>();
que.offer(root);
int node=1;
int level=1;
while(!que.isEmpty()){
root=que.poll();
--node;
if(root.left==null&&root.right==null){
return level;
}
if(root.left!=null){
que.offer(root.left);
}
if(root.right!=null){
que.offer(root.right);
}
if(node==0){
node=que.size();
++level;
}
}
return level;
}
}