Count Complete Tree Nodes leetcode

Given a complete binary tree, count the number of nodes.

Definition of a complete binary tree from Wikipedia:
In a complete binary tree every level, except possibly the last, is completely filled, and all nodes in the last level are as far left as possible. It can have between 1 and 2h nodes inclusive at the last level h.
先找到从root出发到最左和最右的距离, 如果距离相等说明最后一行自左到右都有node 总共2^n - 1个
如果不相等, 递归的找出左右不同的敌方和个数

public class Solution {
    public int countNodes(TreeNode root) {
        if (root == null) {
            return 0;
        }
        int left = findleft(root);
        int right = findright(root);
        if (left == right) {
            return (2<<left - 1) - 1;//减号优先等级大于<<
        } else {
            return countNodes(root.left) + countNodes(root.right) + 1;
        }
    }
    public int findleft(TreeNode root) {
        int res = 0;
        while (root != null) {
            root = root.left;
            res++;
        }
        return res;
    }
    public int findright(TreeNode root) {
        int res = 0;
        while (root != null) {
            root = root.right;
            res++;
        }
        return res;
    }
}