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>

struct elem{
    unsigned int i;
    int v;
};

int partition(
        struct elem* ary,
        int p, int r)
{
    int i =0;
    int j = 0;
    struct elem x, buf;
    x = ary[r];
    i = p;
    for (j = p; j < r; j++) {
        if (ary[j].v <= x.v) {
            buf = ary[j];
            ary[j] = ary[i];
            ary[i] = buf;
            i++;
        }
    }
    buf = x;
    ary[r] = ary[i];
    ary[i] = buf;
    return i;
}

void quick_arg_sort(
        const double *ary,
        int *sorted_index) {
}


struct elem A[100100];
int main() {
    int i, n, k;
    scanf("%d", &n);
    for (i = 0; i < n; i++) {
        scanf("%d", &(A[i].v));
    }
    k = partition(A, 0, n-1);
    for (i = 0; i < n; i++) {
        if (i) {
            printf(" ");
        }
        if (i == k) {
            printf("[");
        }
        printf("%d", A[i].v);
        if (i == k) {
            printf("]");
        }
    }
    printf("\n");
    return 0;
}