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>          // printf(), scanf(), getc(), ungetc()
#include <ctype.h>          // isdigit()
#include <stdbool.h>

#define MAX_N 2000000
#define swap(a, b) { int t; t = a; a = b; b = t; }

int heap[MAX_N];
int sz;

int
extract()
{
	int res = heap[0];
	int x = heap[--sz];
	int i = 0;
	while (i * 2 + 1 < sz)
	{
		int a = i * 2 + 1, b = i * 2 + 2;
		if (b < sz && heap[b] > heap[a])
			a = b;

		if (heap[a] <= x)
			break;

		heap[i] = heap[a];
		i = a;
	}

	heap[i] = x;
	return res;
}

void
insert(int x)
{
	int i = sz++;
	while (i > 0)
	{
		int p = (i - 1) / 2;
		if (heap[p] >= x)
			break;

		heap[i] = heap[p];
		i = p;
	}

	heap[i] = x;
}

int
main(int argc, char** argv)
{
	char command[8];
	int key;
	int n;
	int c;

	sz = 0;
	while (true)
	{
		scanf("%s", command);
		if (command[0] == 'e' && command[1] == 'n')
			break;

		else if (command[0] == 'e' && command[1] == 'x')
			printf("%d\n", extract());

		else if (command[0] == 'i')
		{
			n = 0;
			c = getc(stdin);
			while (c == ' ' || c == '\n')
				c = getc(stdin);
			
			while (isdigit(c))
			{
				n = 10 * n + c - '0';
				c = getc(stdin);
			}

			ungetc(c, stdin);
			key = n;
			insert(key);
		}
	}

	return 0;
}