Get a subset of [1, 2, ... n], by the Reverse Search Method. (Input is n.)

n_subset.c

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

void ReverseSearch(int x[], int i, int n){
    int j;  

    printf("{ ");
    if(i == 0)printf("{} ");//Empty set
    for(j = 1; j <= n ; j++){       
        if(x[j] == 1)printf("%d ", j);
    }
    printf("}\n");

    if(i == n){
        return;
    }

    for(j = i + 1; j <= n; j++){
        //Add a element
        x[j] = 1;
        ReverseSearch(x, j, n);
        // Remove a max element of the set.
        x[j] = 0;
    }
}

int main(int argc, char *argv[]){
    int n, j;
    n = atoi(argv[1]); // The input number, n.
    int x[n];

    for(j = 0; j <= n; j++){
        x[j] = 0;
    }
    x[0] = 1;
    ReverseSearch(x, 0, n);
    
    return 0; 
}