二叉树的深度

题目描述

输入一棵二叉树，求该树的深度。从根结点到叶结点依次经过的结点（含根、叶结点）形成树的一条路径，最长路径的长度为树的深度。

思路

时间复杂度O(lgn)，空间复杂度O(lgn)。

递归代码

/**
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
public class Solution {
    public int TreeDepth(TreeNode root) {
        if(root == null)    return 0;
        return Math.max(1+TreeDepth(root.left), 1+TreeDepth(root.right));
    }
}

非递归代码

import java.util.Queue;
import java.util.LinkedList;
/**
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
public class Solution {
    public int TreeDepth(TreeNode root) {
        if(root == null)    return 0;
        int count = 0;
        int width = 1;
        int depth = 0;
        TreeNode curr = null;
        Queue<TreeNode> queue = new LinkedList<TreeNode>();
        queue.offer(root);
        while(queue.size() != 0) {
            curr = queue.poll();
            if(curr.left != null) {
                queue.offer(curr.left);
            }
            if(curr.right != null) {
                queue.offer(curr.right);
            }
            count++;
            if(count == width) {
                depth++;
                count = 0;
                width = queue.size();
            }
        }
        return depth;
    }
}