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>
void swap(int H[], int i, int j){
  int tmp=H[i];
  H[i]=H[j];
  H[j]=tmp;
}
/**************************************************
 *配列array[p..r]をarray[p..q-1]の各要素がarray[q]以下
 array[q+1..r]の各要素がarray[q]より大きい
 *二つの部分に分割し, 添字qを返す
 *
 *
 *
 **************************************************/
int partition(int array[], int p, int r){
  int x=array[r];  //配列の最後の要素, これを基準にしてarrayを二つに分割する
  int i=p-1, j;  //i: x以下の配列の末尾の添字, j : 先頭
  for(j=i+1; j<r; ++j){
	if(array[j]<=x){
	  ++i;
	  swap(array, i, j);
	}
  }
  swap(array, i+1, r);
  return i+1;
}
int main(){
  /*
   *変数
   */
  int length;  //配列Aの長さ
  int A[100005];  //入力値を入れる配列
  int i;  //ループの制御変数
  int q;
  /*
   *数値の読み込み
   */
  /* 長さの読み込み */
  scanf("%d", &length);
  /* 入力値の読み込み */
  for(i=0; i<length; ++i){
	scanf("%d", &A[i]);
  }
  q=partition(A, 0, length-1);
  for(i=0; i<length; ++i){
	if(i!=0)
	  printf(" ");
	if(i==q)
	  printf("[%d]", A[i]);
	else
	  printf("%d", A[i]);
  }
  printf("\n");
  return 0;
}