Question

How to generate all possible permutations of N numbers in C

Answer 1

#include <stdio.h>
#include <stdlib.h>
   
void swap(int *x, int *y) {
    int temp;
    
    temp = *x;
    *x = *y;
    *y = temp;
}

void printArray(int a[], int constant_len) {
    for (int i = 0; i < constant_len; i++)
        printf("%d ", a[i]);
    printf("\n");
}
 
void heapAlgorithmPermutation(int a[], int len, int constant_len) {
    if (len == 1) {
        printArray(a, constant_len);
        return;
    }
 
    for (int i = 0; i < len; i++) {
        heapAlgorithmPermutation(a, len - 1, constant_len);

        if (len % 2 == 1)
            swap(&a[0], &a[len - 1]);
        else
            swap(&a[i], &a[len - 1]);
    }
}

int main(void) {
    int arr[] = {1, 2, 3, 4};

    int len = sizeof arr / sizeof arr[0];

    heapAlgorithmPermutation(arr, len, len);

    return 0;
}




/*
run:

1 2 3 4 
2 1 3 4 
3 1 2 4 
1 3 2 4 
2 3 1 4 
3 2 1 4 
4 2 3 1 
2 4 3 1 
3 4 2 1 
4 3 2 1 
2 3 4 1 
3 2 4 1 
4 1 3 2 
1 4 3 2 
3 4 1 2 
4 3 1 2 
1 3 4 2 
3 1 4 2 
4 1 2 3 
1 4 2 3 
2 4 1 3 
4 2 1 3 
1 2 4 3 
2 1 4 3 

*/

 

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