题解 | #完全二叉树结点数#

import java.util.*;

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

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

    }
}*/
public class Solution {
    public int nodeNum(TreeNode head) {

        // 一些特殊情况的处理
        if (null == head) {
            return 0;
        }
        if (null == head.left && null == head.right) {
            return 1;
        }

        int res = 0; // 定义一个整型变量，用于存放完全二叉树的节点个数
        Queue<TreeNode> queue = new LinkedList<>();
        TreeNode node = head;
        queue.add(node);

        while (!queue.isEmpty()) {
            node = queue.poll();
            res++;
            if (null != node.left) {
                queue.add(node.left);
            }
            if (null != node.right) {
                queue.add(node.right);
            }
        }
        return res;
    }
}