minimun depth of binary tree

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.

这个题跟求最大深度差不多。

使用递归最简单。不使用递归就是在层序遍历的时候判断。。见代码

/**
 * 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;
      /*  if(root.left==null&&root.right==null) return 1;
         if(root.left==null) return minDepth(root.right)+1;
        if(root.right==null) return minDepth(root.left)+1;
        int left=minDepth(root.left);
        int right=minDepth(root.right);
        return Math.min(left,right)+1;
        */
        Queue<TreeNode> q=new LinkedList<>();
        q.add(root);
        int count=1;
        while(!q.isEmpty()){
            int size=q.size();
            for(int i=0;i<size;i++){
                TreeNode node=q.poll();
                if(node.left==null&&node.right==null) return count;
                if(node.left!=null) q.add(node.left);
                if(node.right!=null) q.add(node.right);
            }
            count++;
        }
        return count;
    }
}