Question

How to generate non‑overlapping random ranges (start,end),(start,end) in C

Answer 1

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

static int cmp_int(const void *a, const void *b) {
    int x = *(const int *)a;
    int y = *(const int *)b;
    
    return (x > y) - (x < y);
}

void generate_non_overlapping_random_ranges(int begin, int end, int num_ranges) {
    int count = num_ranges * 2;
    int *points = malloc(count * sizeof(int));
    int used = 0;

    if (!points) {
        fprintf(stderr, "Memory allocation failed\n");
        exit(1);
    }

    srand((unsigned)time(NULL));

    // Generate unique random points, the random numbers is chaotic
    while (used < count) {
        int r = begin + rand() % (end - begin);
        int duplicate = 0;

        for (int i = 0; i < used; i++) {
            if (points[i] == r) {
                duplicate = 1;
                break;
            }
        }

        if (!duplicate)
            points[used++] = r;
    }
    
    for (int i = 0; i < count; i += 2) {
        printf("(%d, %d)\n", points[i], points[i + 1]);
    }
    
    // The ranges increase and become non‑overlapping only after sorting
    qsort(points, count, sizeof(int), cmp_int);

    // Once sorted, we pair them 
    for (int i = 0; i < count; i += 2) {
        printf("(%d, %d)\n", points[i], points[i + 1]);
    }

    free(points);
}

int main(void) {
    int start = 1;
    int end = 500;
    int num_ranges = 8;

    generate_non_overlapping_random_ranges(start, end, num_ranges);
    
    return 0;
}



/*
run:

(36, 49)
(59, 84)
(92, 149)
(160, 164)
(277, 297)
(304, 410)
(454, 455)
(466, 489)

*/

 

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