Problem:
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Priority Queue

A priority queue is a data structure which maintains a set $S$ of elements, each of with an associated value (key), and supports the following operations:

$insert(S, k)$: insert an element $k$ into the set $S$

$extractMax(S)$: remove and return the element of $S$ with the largest key

Write a program which performs the $insert(S, k)$ and $extractMax(S)$ operations to a priority queue $S$.
The priority queue manages a set of integers, which are also keys for the priority.

Input

Multiple operations to the priority queue $S$ are given. Each operation is given by "insert $k$", "extract" or "end" in a line. Here, $k$ represents an integer element to be inserted to the priority queue.

The input ends with "end" operation.

Output

For each "extract" operation, print the element extracted from the priority queue $S$ in a line.

Constraints

The number of operations $\leq 2,000,000$

$0 \leq k \leq 2,000,000,000$

Sample Input 1

insert 8
insert 2
extract
insert 10
extract
insert 11
extract
extract
end

Sample Output 1

8
10
11
2

Solution in C (judge verdict: Accepted)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void maxHeapify(int*, int, int);
void insert(int*, int*, int);
int extractMax(int*, int*);
void swap(int *, int *);

main(){
  int h=0, key, S[2000000];
  char txt[8];

  while(1){
    scanf("%s", txt);

    if(strcmp(txt, "end") == 0) break;
    else if(strcmp(txt, "extract") == 0){
      printf("%d\n", extractMax(S, &h));
    }
    else if(strcmp(txt, "insert") == 0){
      scanf("%d", &key);
      insert(S, &h, key);
    }
  }

  return 0;
}

void maxHeapify(int *A, int h, int i){
  int largest = i;
  int l = i*2;
  int r = i*2 + 1;

  if(l<=h && A[l] > A[i]) largest = l;
  if(r<=h && A[r] > A[largest]) largest = r;

  if(largest != i){
    swap(A+largest, A+i);
    maxHeapify(A, h, largest);
  }
}

void insert(int *S, int *h, int key){
  int i;
  int me;

  S[(*h)+1] = key;
  (*h)++;

  me = *h;

  for(i=*h/2; i>=1; i=i/2){
    if(S[me] <= S[i]) break;
    else{
      swap(S+me, S+i);
      me = i;
    }
  }
}

int extractMax(int *S, int *h){
  int res = S[1];

  S[1] = S[*h];
  (*h)--;

  maxHeapify(S, *h, 1);
  return res;
}

void swap(int *a, int *b){
  int tmp;

  tmp = *a;
  *a = *b;
  *b = tmp;
}