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_LENGTH 100000
int Arr[MAX_LENGTH]={0};
int n=0;
int b = 0;
int Partition(int Arr[], int p, int r)
{
    int x=Arr[r];
    int i=p-1;
    for(int j=p;j<r;j++)
    {
        if(Arr[j]<=x)
        {
            i+=1;
            int temp=Arr[i];
            Arr[i]=Arr[j];
            Arr[j]=temp;
        }
    }
    int t = Arr[i+1];
    Arr[i+1]=Arr[r];
    Arr[r]=t;
    return i+1;
}
int main(int argc, const char * argv[]) {
    scanf("%d", &n);
    for(int i=0;i<n;i++){scanf("%d ", &Arr[i]);}
    b=Partition(Arr, 0, n-1);
    for(int i=0;i<n;i++)
    {
        if(i==n-1){printf("%d\n", Arr[i]);}
        else if(i==b){printf("[%d] ", Arr[i]);}
        else{printf("%d ", Arr[i]);}
    }
    return 0;
}