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+1Note that, in this algorithm, Partition always selects an element A[r] as a pivot element around which to partition the array A[p..r].
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.
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 [ ].
12 13 19 9 5 12 8 7 4 21 2 6 11
9 5 8 7 4 2 6 [11] 21 13 19 12