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>

#define MAX 100000

void swap(int *,int *);
int partition(int *,int,int);


int main()
{
  int w[MAX],a,i,c;
  
  scanf("%d",&a);
  
  for(i=0;i<a;i++)scanf("%d",&w[i]);
  
  c = partition(w,0,a-1);
  
  for(i=0;i<a;i++){
    if(i==c){
      printf("[%d] ",w[i]);
      continue;
    }
    
    if(i!=a-1)printf("%d ",w[i]);
    else printf("%d\n",w[i]);
      }
  
  return 0;
}


void swap(int *s,int *t)
{
  int r = *s;
  
  *s=*t;
  *t=r;
}

int partition(int *x,int y,int z)
{
  int k=x[z],i=y-1,j;
  
  for(j=y;j<z;j++){
    if(x[j]<=k){
      i++;
      swap(&x[i],&x[j]);
    }
  }
  
  swap(&x[i+1],&x[z]);
  
  return i+1;
}