Uppgift5wrkimg

/* Program has 1 function swaps() that puts negative elements in the
leftmost indices, and positive elements in the rightmost indices.
It does not necessarily order the elements by size however.
It uses two pointers that start by pointing to the beginning
and end of the array. When the two pointers meet, the swapping is done.*/

#include <stdio.h>
#include <stdlib.h>
#define N 8 // some arbitrary array length just for testing

// Takes an array as parameter, modifies its elements, and returns the modified array
int* swaps(int* array);

void main(){

    // Create and initialize an int array
    int i;
    int *array = malloc(sizeof(int)*N);
    // remember to add spacebar between input integers
    for(i = 0; i < N; i++){
       scanf("%d", &array[i]);
    }

    // Print before swapping
    for(i = 0; i < N; i++){
       printf("[");
       printf("%d", array[i]);
       if(i == N-1){
       printf("] ");
       } else {
       printf("],");
       }
    }
    printf("\n");
    // Call swaps with argument being the newly created array of length N
    swaps(array);

    // Print after swapping
    for(i = 0; i < N; i++){
	printf("[");
        printf("%d", array[i]);
	if(i == N-1){
        printf("] ");
        } else {
        printf("],");
        }
    }
	printf("\n");
}

// Time complexity is O(n^2), however this problem should be able to solve in O(n)
int* swaps(int* array){

    int* ptr1;
    ptr1 = &array[0];
    int* ptr2;
    ptr2 = &array[N-1];
    int tmp;


    for(ptr1; ptr1 <= &array[N-1]; ptr1++){
         if(ptr1==ptr2){
             return array;
         }
         if(*ptr1 >= 0){
             for(ptr2; ptr2 >= &array[0]; ptr2--){
		if(ptr1==ptr2){
             	  return array; // have to check ptr2==ptr1 all the time, otherwise ptr2 will keep iterating
         	}

                // swap elements that ptr1 and ptr2 point to
                if(*ptr2 < 0){
                tmp = *ptr2;
                *ptr2 = *ptr1;
                *ptr1 = tmp;
                ptr2--;
	        if(ptr1==ptr2){
             	   return array; // have to check ptr2==ptr1 after ptr 2 decr, otherwise ptr2 will keep iterating
         	}
                break;
                }
             }
         }
    }
}