void widthFirstTraverse(TNode* root) {
  queue<TNode*> q;   // 隊(duì)列
  q.enqueue(root);
  TNode* p;
  while(q.hasElement()) {
   p = q.dequeue();  // 隊(duì)首元素出隊(duì)列
   visit(p);     // 訪問(wèn)p結(jié)點(diǎn)
   if(p->left)
     q.enqueue(p->left);
   if(p->right)
     q.enqueue(p->right);
  } 
}

void preTraverse(TNode* root) {
  if(!root)
   return;
  visit(root);
  preTraverse(root->left);
  preTraverse(root->Right);
}

void preTraverseNonRecursive(TNode* root) {
  stack<TNode> stack;  // 棧
  stack.push(root);
  TNode* p;
  while(!stack.isEmpty()) { // 棧非空
   p = stack.pop();
   visit(p);
   if(p->pRight)
     s.push(p->pRight);
   if(p->pLeft)
     s.push(p->pLeft);
  }
}