perm.c

#include <stdio.h>
#include <stdlib.h>
#include <limits.h>

#define N 100

// Returns an integer from [a,b] using library function rand() and operator %
// if a > b return INT_MIN
// if b - a > RAND_MAX return INT_MAX
// if a == b return a
// else return integer from [a,b]
int rand_from_interval(int a, int b) {
	if (a > b) return INT_MIN;
	else if ((b - a) > RAND_MAX) return INT_MAX;
	else if (a == b) return a;
	else return rand() % (b - a + 1) + a;
}

void swap (int array[], int i, int k) {
	int tmp = array[i];
	array[i] = array[k];
	array[k] = tmp;
}

// random permutation of integers from [0, n-1]
void rand_permutation(int n, int array[]) {
	if (n < 0) return;

	for (int i = 0; i < n; i++){
		array[i] = i;
	}

	for (int i = 0; i < n - 1; i++){
		int k = rand_from_interval(i, n - 1);
		swap(array, i, k);
	}
}

// bubble sort (increasing order)
// returns number of iterations of the external loop
// after which the array is sorted
// for { 0 1 2 3 7 4 5 6 } -> 1,
// for { 1 2 3 7 4 5 6 0 } -> 7,
// for { 0 1 2 3 4 5 6 7 } -> 0.
int bubble_sort(int n, int array[]) {
	int cnt = -1;
	int flag = 1;

	while (flag){
		flag = 0;
		cnt++;
		int i = 0;

		while (i < n - 1){
			if (array[i] > array[i + 1]){
				swap(array, i, i + 1);
				flag = 1;
			}
			i++;
		}
	}

	return cnt;
}

int main(void) {
	int to_do, seed;
	int a, b, m, n;
	int array[N];

	scanf("%d %d", &to_do, &seed);
	srand((unsigned) seed); // set the seed

	switch(to_do) {
		case 1:
			scanf("%d %d %d",&a, &b, &m);
			for(int i = 0; i < m; ++i) {
				printf("%d ", rand_from_interval(a, b));
			}
			printf("\n");
			break;
		case 2:
			scanf("%d", &n);
			rand_permutation(n, array);
			for(int i = 0; i < n; ++i) printf("%d ", array[i]);
			printf("\n");
			break;
		case 3:
			scanf("%d", &n);
			rand_permutation(n, array);
			printf("%d\n", bubble_sort(n, array));
			break;
		default:
			printf("NOTHING TO DO!\n");
			break;
	}
	return 0;
}