LeetCode Count Complete Tree Nodes

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

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 2^h nodes inclusive at the last level h.

思路：
我们只需要看左子树是不是满的，如果满，我们递归分析右子树；如果左子树不满，我们递归分析左子树。

代码：

int countNodes(TreeNode* root) {
        if(root == NULL) return 0;
        int num = 1;
        TreeNode *curL = root -> left, *curR = root -> left;
        while(curR){
            curL = curL -> left;
            curR = curR -> right;
            num = num << 1;
        }
        return num + ((!curL) ? countNodes(root -> right) : countNodes(root -> left));
    }

注：使用了位运算，效率高。