PAT 1064 Complete Binary Search Tree

 #include <iostream>
 #include <cstdio>
 #include <cstdlib>
 #include <vector>
 #include <algorithm>

 using namespace std;

 class Node {
 public:
     int val;
     Node* left;
     Node* right;
 public:
     Node(): val(), left(NULL), right(NULL) {}
     Node(int _val, Node* _left = NULL, Node* _right = NULL): val(_val), left(_left), right(_right) {}
 };

 vector<Node*> build_next_level(vector<Node*> last_level, int &num) {
     vector<Node*> res;
     if (num < ) return res;

     for (auto iter = last_level.begin(); iter != last_level.end(); iter++) {
         Node* parent = *iter;

         Node* lchild = new Node();
         res.push_back(lchild);
         parent->left = lchild;
         if (--num < ) break;

         Node* rchild = new Node();
         res.push_back(rchild);
         parent->right= rchild;
         if (--num < ) break;
     }

     return res;
 }

 void inorder_traverse(Node* root, int& order) {
     if (root == NULL) return;
     inorder_traverse(root->left, order);
     root->val = order++;
     inorder_traverse(root->right, order);
 }

 int main() {
     int cnt;

     scanf("%d", &cnt);

     vector<int> nums(cnt, );

     if (cnt < ) return ;

     for (int i = ; i<cnt; i++) {
         int num = ;
         scanf("%d", &num);
         nums[i] = num;
     }
     sort(nums.begin(), nums.end());

     vector<vector<Node*> > levels;

     vector<Node*> last_level;
     last_level.push_back(new Node());

     levels.push_back(last_level);

     int node_cnt = cnt - ; // we already pushed the root node
     while (node_cnt > ) {
         vector<Node*> cur_level = build_next_level(last_level, node_cnt);
         levels.push_back(cur_level);
         swap(last_level, cur_level);
     }

     int order = ;
     inorder_traverse(levels[][], order);

     node_cnt = cnt;

     for (auto iter_levels = levels.begin(); iter_levels != levels.end(); iter_levels++) {
         vector<Node*>& cur_level = *iter_levels;
         for (auto iter = cur_level.begin(); iter != cur_level.end(); iter++) {
             Node* node = *iter;
             int val = nums[node->val];
             if (--node_cnt > ) {
                 printf("%d ", val);
             } else {
                 printf("%d\n", val); // last element
             }
         }
     }
     return ;
 }

又是跟书本比较近的一题