C++ Operations on a Sequence

Suppose, we are given an empty sequence and n queries that we have to process. The queries are given in the array queries and they are in the format {query, data}. The queries can be of the three following types−

• query = 1: Add the supplied data to the end of the sequence.

• query = 2: Print the element at the beginning of the sequence. After that delete the element.

• query = 3: Sort the sequence in ascending order.

Note that, query types 2 and 3 always have data = 0.

So, if the input is like n = 9, queries = {{1, 5}, {1, 4}, {1, 3}, {1, 2}, {1, 1}, {2, 0}, {3, 0}, {2, 0}, {3, 0}}, then the output will be 5 and 1.

The sequence after each query is given below −

• 1: {5}
• 2: {5, 4}
• 3: {5, 4, 3}
• 4: {5, 4, 3, 2}
• 5: {5, 4, 3, 2, 1}
• 6: {4, 3, 2, 1} , Prints 5.
• 7: {1, 2, 3, 4}
• 8: {2, 3, 4}, Prints 1.
• 9: {2, 3, 4}

To solve this, we will follow these steps −

priority_queue<int> priq
Define one queue q
for initialize i := 0, when i < n, update (increase i by 1), do:
   operation := first value of queries[i]
   if operation is same as 1, then:
      x := second value of queries[i]
      insert x into q
   otherwise when operation is same as 2, then:
      if priq is empty, then:
         print first element of q
         delete first element from q
      else:
         print -(top element of priq)
         delete top element from priq
    otherwise when operation is same as 3, then:
       while (not q is empty), do:
          insert (-first element of q) into priq and sort
          delete element from q

Example

Let us see the following implementation to get better understanding −

#include <bits/stdc++.h>
using namespace std;

void solve(int n, vector<pair<int, int>> queries){
   priority_queue<int> priq;
   queue<int> q;
   for(int i = 0; i < n; i++) {
      int operation = queries[i].first;
      if(operation == 1) {
         int x;
         x = queries[i].second;
         q.push(x);
      } else if(operation == 2) {
         if(priq.empty()) {
             cout << q.front() << endl;
             q.pop();
         } else {
            cout << -priq.top() << endl;
            priq.pop();
         }
      } else if(operation == 3) {
         while(!q.empty()) {
            priq.push(-q.front());
            q.pop();
         }
      }
   }
}
int main() {
   int n = 9; vector<pair<int, int>> queries = {{1, 5}, {1, 4}, {1, 3}, {1, 2}, {1, 1}, {2, 0},  {3, 0}, {2, 0}, {3, 0}};
   solve(n, queries);
   return 0;
}

Input

9, {{1, 5}, {1, 4}, {1, 3}, {1, 2}, {1, 1}, {2, 0}, {3, 0}, {2, 0}, {3, 0}}

Output

5
1