day53（1.4）——leetcode面试经典150

222. 完全二叉树的节点个数

我感觉会有更简单的方法，但是我不知道，我这几题二叉树，只有一题是用bfs，所以这题我也用了bfs

222. 完全二叉树的节点个数

题目：

题解：

/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode() {} * TreeNode(int val) { this.val = val; } * TreeNode(int val, TreeNode left, TreeNode right) { * this.val = val; * this.left = left; * this.right = right; * } * } */ class Solution { public int countNodes(TreeNode root) { int sum=0; if(root == null) { return 0; } Queue<TreeNode> queue = new LinkedList<>(); queue.offer(root); sum++; while(queue.size() > 0) { //poll是取出并移除，peek是查看 TreeNode treeNode = queue.poll(); if(treeNode.left != null) { queue.offer(treeNode.left); sum++; } if(treeNode.right != null) { queue.offer(treeNode.right); sum++; } } return sum; } }