#include <queue>

using namespace std;

int calculateTreeHeight(Node *root)
{
 if(root == NULL)
  return 0;
 int visitedNumber = 0;
 int enQueNumber = 1; //當前入棧的序號，root為1
 int lastLevelNumber = 1;
 int height = 0;

 queue<Node*> q;
 q.push(root);
 while(!q.empty())
 {
  Node *node = q.front();
  q.pop();
  visitedNumber++;

  if(node->left != NULL)
  {
   q.push(node->left);
   enQueNumber++;
  }
  if(node->right != NULL)
  {
   q.push(node->right);
   enQueNumber++;
  }

  //訪問到當前level上的最後一個節點
  if(visitedNumber == lastLevelNumber)
  {
   height++;
   lastLevelNumber = enQueNumber;
  }
 }
 return height;
}