Problem:
Partition

Quick sort is based on the Divide-and-conquer approach. In QuickSort(A, p, r), first, a procedure Partition(A, p, r) divides an array A[p..r] into two subarrays A[p..q-1] and A[q+1..r] such that each element of A[p..q-1] is less than or equal to A[q], which is, inturn, less than or equal to each element of A[q+1..r]. It also computes the index q.

In the conquer processes, the two subarrays A[p..q-1] and A[q+1..r] are sorted by recursive calls of QuickSort(A, p, q-1) and QuickSort(A, q+1, r).

Your task is to read a sequence A and perform the Partition based on the following pseudocode:

Partition(A, p, r)
1 x = A[r]
2 i = p-1
3 for j = p to r-1
4 do if A[j] <= x
5 then i = i+1
6 exchange A[i] and A[j]
7 exchange A[i+1] and A[r]
8 return i+1

Note that, in this algorithm, Partition always selects an element A[r] as a pivot element around which to partition the array A[p..r].

Input

The first line of the input includes an integer n, the number of elements in the sequence A.

In the second line, Ai (i = 1,2,...,n), elements of the sequence are given separated by space characters.

Output

Print the sorted sequence. Two contiguous elements of the sequence should be separated by a space character. The element which is selected as the pivot of the partition should be indicated by [  ].

Constraints

1 ≤ n ≤ 100,000

0 ≤ Ai ≤ 100,000

Sample Input 1

12
13 19 9 5 12 8 7 4 21 2 6 11

Sample Output 1

9 5 8 7 4 2 6 [11] 21 13 19 12

Solution in C (judge verdict: Accepted)

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

#define SWAP(a, b, v) v = a, a = b, b = v

int
partition(int *a, int p, int r)
{
	int x = a[r];
	int i, v;

	for (i = p; i < r; i++) {
		if (a[i] > x)
			continue;

		SWAP(a[p], a[i], v);
		p++;
	}

	SWAP(a[p], a[r], v);

	return p;
}

int
main(void)
{
	int i, n, q;
	int *a;

	scanf("%d", &n);

	a = (int *)malloc(sizeof(int) * n);
	if (a == NULL)
		return 1;

	for (i = 0; i < n; i++)
		scanf("%d", a + i);

	q = partition(a, 0, n - 1);

	for (i = 0; i < q; i++)
		printf("%s%d", i ? " " : "", a[i]);
	printf(" [%d]", a[i++]);
	for (; i < n; i++)
		printf(" %d", a[i]);
	puts("");

	return 0;
}