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.*;

class Main {
        public static void main(String args[]) {
                try (Scanner sc = new Scanner(System.in)) {
                        int N = sc.nextInt();
                        int[] A = new int[N];
                        for (int i = 0; i < N; i++) {
                                A[i] = sc.nextInt();
                        }

                        int x = A[N - 1];
                        int i = -1;
                        for (int j = 0; j < N - 1; j++) {
                                if (A[j] <= x) {
                                        i++;
                                        int tmp = A[i];
                                        A[i] = A[j];
                                        A[j] = tmp;
                                }
                        }
                        int tmp = A[i + 1];
                        A[i + 1] = A[N - 1];
                        A[N - 1] = tmp;
                        for (int k = 0; k < N; k++) {
                                if (k == i + 1) {
                                        System.out.print("["+A[k]+"]");
                                } else {
                                        System.out.print(A[k]);
                                }
                                if (k == N - 1) {
                                        System.out.print("\n");
                                } else {
                                        System.out.print(" ");
                                }
                        }
                }
        }
}