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。

Solution1://递归，最简洁

public class Solution {

    public int TreeDepth(TreeNode root) {

        if (root == null)

            return 0;

        int left = TreeDepth(root.left);

        int right = TreeDepth(root.right);

        return Math.max(left, right) + 1;

    }

}

Solution2://一层层的遍历tree

public class Solution {

    public int TreeDepth(TreeNode root) {

        if (root == null)

            return 0;

        Queue<TreeNode> queue = new LinkedList<>();

        queue.offer(root);

        int depth = 0;

        int count = 0; //记录此时从queue中取出的节点个数

        int nextCount = 1; //记录当前层的节点个数

        while (queue.size() != 0) {

            TreeNode top = queue.poll();

            count++; //每取出一个节点，count加一

            if (top.left != null)

                queue.offer(top.left);

            if (top.right != null)

                queue.offer(top.right);

            if (count == nextCount) { //此时该层节点都被取出

                nextCount = queue.size();  //把下一层的节点总数赋给nextCount

                count = 0;

                depth++;

            }

        }

        return depth;

    }

}