and add the resulting points (if not there already) to an array.
   The answer to Part One is the number of elements in the array
TODO: I don't like my `linearize2d` thing! Thinking of a replacement
===================================================================== */

void aoc202408(char *data, size_t len) {
    (void)len; // unused argument
    struct TextGrid tg;
    tg.data = data;
    tg.cols = strchr(data, '\n') - data + 1;
    tg.rows = tg.cols - 1; // rows includes the '\n'
    #if 0
    unsigned anti[256][2]; // locations of antinodes
    unsigned nanti = 0;
    unsigned size = 1 + strchr(data, '\n') - data;
    for (unsigned row = 0; row < size-1; row++) {
        for (unsigned col = 0; col < size-1; col++) {
            char *p = data + linearize2d(size, row, col);
            if (*p != '.') {

                    }
                    q = strchr(q + 1, *p);
                }
            }
        }
    }
    printf("There are %u antinodes within the map.\n", nanti);
    #endif
}

/* === aoc202407 =======================================================
   Part one looks easy
   Part two also easy
 ===================================================================== */

#ifndef AOCUTILS_H_INCLUDED
#define AOCUTILS_H_INCLUDED

#include <stdbool.h>

struct TextGrid {
    unsigned rows, cols;
    char *data; // may have '\n' at end of rows
};

bool TGvalid(struct TextGrid *tg, unsigned row, unsigned col);