My code does not run fully

Question

Good evening, folks. I need to implement a program that always prints a sequence of three numbers where there can be no repetition.

Ex.: t = 4.

Expected output: (0 1 2) (0 1 3) (0 2 3) (1 2 3)

The program runs for t = 4, however, for t = 10, it runs only to some extent (up to i = 6). I’ve tested every part of the code and I can’t find the error, I wonder if someone could help me?

Thank you! :)

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

typedef struct{
  int v1;
  int v2;
  int v3;
}Triangulo;

int main(){
int n;
scanf("%d", &n);

Triangulo T[n];

int t;
t = (n*(n-1)*(n-2))/6;
printf("t = %d\n", t);

int c = 0;
int f = c+1;
int s = f+1;

for(int i = 0; i < t; i++){
  T[i].v1 = c;
  T[i].v2 = f;
  T[i].v3 = s;

if(s != n-1){
  s++;
}else if((s == n-1)&&(f == n-2)){
  c++;
  f = c+1;
  s = f+1;
}else if(s == n-1){
  f++;
  s = f+1;
}
}

for(int j = 0; j < t; j++){
  printf("%d %d %d\n", T[j].v1, T[j].v2, T[j].v3);
}


  return 0;
}

Answer 1

You want all permutations that are of the type (i j k) such that i < j < k, correct? You won’t be able to do this using just one for. Note that when we set values for i and j, for example, we still have the values of j+1 until t-1 to assign the k. Let’s take an example:

Consider that at a certain point in the algorithm i = 1 and j = 3, and that t = 10. The possible sequences fixing these values would be:

(1 3 4)
(1 3 5)
(1 3 6)
(1 3 7)
(1 3 8)
(1 3 9)

Note that we need a for that goes from j+1 until t-1 only to iterate the possible values of k. Similarly, if we fix only the value i, we need a for to go through the possible values for j and, for each value of j, a new for for values of k. I think it’s clear that we need a for for each variable.

Follows an implementation:

#include <stdio.h>

int main(void) {

    int t;

    scanf("%d", &t);

    // Considera todos os valores de 0 até t-1
    for(int i = 0; i < t; i++){

        // Considera todos os valores de i+1 até t-1 para impedir que os valores se repitam
        for(int j = i+1; j < t; j++){

            // Considera todos os valores de j+1 até t-1 para impedir que os valores se repitam
            for(int k = j+1; k < t; k++){
                printf("(%d %d %d) ", i, j, k);
            }
        }
    }

    printf("\n");
    return 0;
}

Demonstration here.