二叉树的深度

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

解题思路

递归写法，比较简单

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; } }

非递归写法

depth 是当前结点所在的层数，count 是已经遍历过的结点数，nextCount 是下层的结点总数，当 count == nextCount 的时候，代表本层的节点已经遍历完毕

import java.util.LinkedList; import java.util.Queue; public class Solution { public int TreeDepth(TreeNode root) { if(root == null) { return 0; } Queue<TreeNode> queue = new LinkedList<>(); queue.add(root); int depth = 0, count = 0, nextCount = 1; while(queue.size() != 0) { TreeNode top = queue.poll(); count++; if(top.left != null) { queue.add(top.left); } if(top.right != null) { queue.add(top.right); } if(count == nextCount) { nextCount = queue.size(); count = 0; depth++; } } return depth; } }