How would you display an array of integers as a set of ranges? (algorithm)

Question

Given an array of integers, what is the simplest way to iterate over it and figure out all the ranges it covers? for example, for an array such as:

$numbers = ar         


        

Answer 1

C (gcc)

It is similar to the Python's version.

void ranges(int n; int a[n], int n)
{
  qsort(a, n, sizeof(*a), intcmp);
  for (int i = 0; i < n; ++i) {
    const int start = i;
    while(i < n-1 and a[i] >= a[i+1]-1)
      ++i;
    printf("%d", a[start]);
    if (a[start] != a[i])
      printf("-%d", a[i]);
    if (i < n-1)
      printf(",");
  }
  printf("\n");
}

Example:

/**
 * $ gcc -std=c99 -Wall ranges.c -o ranges && ./ranges
 */
#include  // and
#include 
#include 

#define T(args...)                                              \
  {                                                             \
    int array[] = {args};                                       \
    ranges(array, sizeof(array) / sizeof(*array));              \
  }

int intcmp(const void* a, const void* b)
{
  const int *ai = a;
  const int *bi = b;

  if (*ai < *bi)
    return -1;
  else if (*ai > *bi)
    return 1;
  else
    return 0;
}

int main(void)
{
  T(1,3,4,5,6,8,11,12,14,15,16);
  T();
  T(1);
  T(1, 2);
  T(3, 1);
  T(1, 3, 4);
  T(1, 2, 4);
  T(1, 1, 2, 4);
  T(1, 2, 2, 4);
  T(1, 2, 2, 3, 5, 5);
}

Output:

1,3-6,8,11-12,14-16

1
1-2
1,3
1,3-4
1-2,4
1-2,4
1-2,4
1-3,5