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>

int main(){
  int n,i,x,j,r,t;
  int *a;
  scanf("%d",&n);
   a = malloc(sizeof(int)*n+1);

   for(i = 0; i < n; i++){
     scanf("%d",&a[i]);
   }
   x = a[i-1];
   r = i-1;
   i = 0 - 1;
   for(j = 0; j < r; j++){
     if( a[j] <= x){
       i = i + 1;
       t = a[j];
       a[j] = a[i];
       a[i] = t;
     }
   }
     t = a[i+1];
     a[i+1] = a[r];
     a[r] = t;
   

   for ( j = 0; j < n; j++){
     if( j == i+1){
       printf("[");
     }
     printf("%d",a[j]);
     if(j == i+1){
       printf("]");
     }
     if(j < n-1){
       printf(" ");
     }
   }
   printf("\n");
   return 0;
}