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)

#define dbg(fmt,...) fprintf(stderr,fmt,__VA_ARGS__)
#define dpri(x) dbg(#x ": %d\n", x)
#define dprs(x) dbg(#x ": %s\n", x)
#include <stdio.h>
typedef long long ll;
const int MYINF = 1e9+7;
typedef int bool;
const bool true = 1;
const bool false = 0;

#define MAX_N 100010

#define exchange(a, b) exchange_(&(a), &(b))
void exchange_(int *a, int *b) {
	int tmp = *a;
	*a = *b;
	*b = tmp;
}

int Partition(int *A, int p, int r) {
	int x = A[r];
	int i = p - 1, j;
	for (j = p; j < r; j++) {
		if (A[j] <= x) {
			i++;
			exchange(A[i], A[j]);
		}
	}
	exchange(A[i+1], A[r]);
	return i+1;
}

int arr[MAX_N];
int n;

int main(int argc, char **argv)
{
	int i, p;
	scanf("%d", &n);
	for (i = 0; i < n; i++) {
		scanf("%d", &arr[i]);
	}

	p = Partition(arr, 0, n-1);

	const char *fmt, *sp = "";
	for (i = 0; i < n; i++) {
		if (i == p) {
			fmt = "%s[%d]";
		} else {
			fmt = "%s%d";
		}
		printf(fmt, sp, arr[i]);
		sp = " ";
	}
	putchar('\n');
	return 0;
}