Permute array.c

#include <math.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
#include <limits.h>
#include <stdbool.h>

void permute(int *, int, int);

void permute(int *a, int n, int k) {
  // reduce complexity
  k = k % n;

  /// special cases instant result
  if (n <= 1) { return; }
  if (n == k) { return; }

  // store first elements
  int *first_elems = calloc(k, sizeof(int));
  for (int i = 0; i < k; i++) {
    first_elems[i] = a[i];
  }

  // permute the rest
  for (int i = 0; i < n - k; i++) {
    a[i] = a[i+k];
  }

  // append first element to end
  for (int i = 0; i < k; i++) {
    a[n-k+i]= first_elems[i];
  }
}

int main(){
  int n;
  int k;
  scanf("%d %d",&n,&k);
  int *a = malloc(sizeof(int) * n);
  for(int a_i = 0; a_i < n; a_i++){
    scanf("%d",&a[a_i]);
  }
  permute(a, n, k);
  for (int j = 0; j < n; j++) {
    printf("%d ", a[j]);
  }
  return 0;
}

/*
1 2 3 4 5 6 7 8 9
2 3 4 5 6 7 8 9 1
3 4 5 6 7 8 9 1 2
4 5 6 7 8 9 1 2 3
5 6 7 8 9 1 2 3 4
 
 take k first elements
 shift with override all k till n - k - 1 elements by k to left
 append k first elements to end
*/