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 {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param head TreeNode类 
     * @return int整型
     */
    public int nodeNum (TreeNode head) {
        // write code here
        //层序遍历
        if(head == null) return 0;

        int res = 0;
        Queue<TreeNode> queue = new LinkedList<TreeNode>();
        queue.add(head);

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