[LeetCode][JavaScript]Count Complete Tree Nodes

Count Complete Tree Nodes

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 2hnodes inclusive at the last level h.

https://leetcode.com/problems/count-complete-tree-nodes/

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Tricky的做法，往左找到最深的叶子节点，往右再找最深的叶子节点。

如果他们的深度一样，说明是棵完全二叉树，节点数套用公式2^n - 1。

否则再用同样的方法递归这个点的左子树和右子树。

犯2把循环条件写成了while(leftChild && leftChild.val)，val可能是0，结果就不对了ORZ。

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
var countNodes = function(root) {
    return treeNodes(root);

    function treeNodes(node){
        if(!node){
            return 0;
        }else{
            var leftDepth = 0;
            var rightDepth = 0;
            var leftChild = node.left;
            while(leftChild){
                leftDepth++;
                leftChild = leftChild.left;
            }
            var rightChild = node.right;
            while(rightChild){
                rightDepth++;
                rightChild = rightChild.right;
            }
            if(leftDepth === rightDepth){
                return Math.pow(2, leftDepth + 1) - 1;
            }else{
                return treeNodes(node.left) + treeNodes(node.right) + 1;
            }
        }
    }
};