graph.c

// $ cc -o graph graph.c
// $ ./a.out
// Ref: https://old.reddit.com/r/roguelikedev/comments/1b7pa9w/
#include <stdio.h>

static int rand31(unsigned long long *s)
{
    *s = *s*0x3243f6a8885a308dU + 1;
    return (int)(*s >> 33);
}

int main(void)
{
    enum {
        width  = 15,
        height = 13,
    };
    unsigned long long rng[1] = {(size_t)rng};

    // Normally-distributed seed position
    int verts = 1 << __builtin_popcount(rand31(rng) >> 24);

    for (int y = 0; y < height; y++) {
        // Draw vertices
        for (int x = 0; x < width; x++) {
            putchar(verts&(1<<x) ? 'O' : ' ');
            putchar(x==width-1 ? '\n' : ' ');
        }
        if (y == height-1) break;

        // Initialze edge display as all spaces
        char row[2*width+1] = {0};
        for (int x = 0; x < width; x++) {
            row[2*x+0] = row[2*x+1] = ' ';
        }

        int next = 0;
        do {
            // Slanted edges
            for (int x = 0; x < width-1; x++) {
                int left  = verts & (1<<(x+0));
                int right = verts & (1<<(x+1));
                if (left && right) {
                    switch (rand31(rng) >> 28) {
                    case 1: row[2*x+1] = '\\';
                            next |= 1 << (x+1);
                            break;
                    case 2: row[2*x+1] = '/';
                            next |= 1 << x;
                    }
                } else if (left) {
                    if (rand31(rng) >> 29) {
                        row[2*x+1] = '\\';
                        next |= 1 << (x+1);
                    }
                } else if (right) {
                    if (rand31(rng) >> 29) {
                        row[2*x+1] = '/';
                        next |= 1 << x;
                    }
                }
            }

            // Vertical edges
            for (int x = 0; x < width; x++) {
                if (verts & (1<<x)) {
                    if (!(rand31(rng) >> 29)) {
                        row[2*x] = '|';
                        next |= 1 << x;
                    }
                }
            }
        } while (!next);  // must propagate at least one vertex
        puts(row);

        verts = next;
    }
}