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 JAVA (judge verdict: Accepted)

import java.util.Scanner;

class Main {
  public static void main(String... args) {
    Scanner sc = new Scanner(System.in);
    int size = Integer.parseInt(sc.next());
    int[] array = new int[size];
    for (int i = 0; i < size; i++) {
      array[i] = Integer.parseInt(sc.next());
    }
    int p = 0;
    int center = array[size-1];
    Partition(array, 0, size-1);
  }

  public static int Partition(int[] array, int p, int r) {
    int x = array[r];
    int i = p - 1;
    int tmp;
    for (int j = p; j < r; j++) {
      if (array[j] <= x) {
        tmp = array[++i];
        array[i] = array[j];
        array[j] = tmp;
      }
    }
    tmp = array[i + 1];
    array[i + 1] = array[r];
    array[r] = tmp;

    int size = array.length;
    for (int index = 0; index < size; index++) {
      if (index == i + 1) {
        System.out.print("[" + array[index] + "] ");
      } else if (index == size - 1) {
        System.out.println(array[index]);
      } else {
        System.out.print(array[index] + " ");
      }
    }

    return i + 1;
  }
}