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
        pre( head);
        return c;
    }

    int c = 0;
    private void pre(TreeNode head) {
        if (head == null) {
            return;
        }
        c++;
        pre( head.left);
        pre( head.right);
    }
}