[leetcode][tree] Count Complete Tree Nodes

/**
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int countNodes(TreeNode* root) {
if(NULL == root) return 0;
TreeNode *p = root->left;
int leftHeight = 0, rightHeight = 0;
//求得左子树的高度
while(p != NULL){
p = p->left;
++leftHeight;
}
//求得右子树的高度
p = root->right;
while(p != NULL){
p = p->right;
++rightHeight;
}
//如果两者等高，则说明是满二叉树，直接计算得到节点个数
if(leftHeight == rightHeight){//满二叉树
return (1 << (leftHeight+1))-1;
}
//如果两者不等高，递归求得左右子树的节点个数，当前树的节点个数等于左右子树节点个数之和加1（根节点）
return 1 + countNodes(root->left) + countNodes(root->right);
}
};