按层次打印二叉树

void printLevelOrder(BinaryTree *root) {
  if (!root) return;
  queue<BinaryTree*> nodesQueue;
  int nodesInCurrentLevel = 1;
  int nodesInNextLevel = 0;
  nodesQueue.push(root);
  while (!nodesQueue.empty()) {
    BinaryTree *currNode = nodesQueue.front();
    nodesQueue.pop();
    nodesInCurrentLevel--;
    if (currNode) {
      cout << currNode->data << " ";
      nodesQueue.push(currNode->left);
      nodesQueue.push(currNode->right);
      nodesInNextLevel += 2;
    }
    if (nodesInCurrentLevel == 0) {
      cout << endl;
      nodesInCurrentLevel = nodesInNextLevel;
      nodesInNextLevel = 0;
    }
  }
}