Index: aoc2024.c
==================================================================
--- aoc2024.c
+++ aoc2024.c
@@ -23,10 +23,29 @@
     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;
+    #endif
+
+    char *p = data;
+    while (*p) {
+        while ((*p == '.') || (*p == '\n')) p++;
+        if (*p) {
+            // p points to an antenna
+            char *q = strchr(p+1, *p);
+            while (q) {
+                // q points to an antenna of the same type as p
+                printf("p is at (C:%u, R:%u); q is at (C:%u, R:%u)\n",
+                      TGcol(&tg, p), TGrow(&tg, p),
+                      TGcol(&tg, q), TGrow(&tg, q));
+                q = strchr(q+1, *p); // next antenna of this type
+            }
+            p += 1;
+        }
+    }
+    #if 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 != '.') {

Index: aocutils.c
==================================================================
--- aocutils.c
+++ aocutils.c
@@ -9,10 +9,16 @@
     return true;
 }
 char *TGcharptr(struct TextGrid *tg, unsigned row, unsigned col) {
     if (!TGvalid(tg, row, col)) return NULL;
     return tg->data + (row * tg->cols) + col;
+}
+unsigned TGcol(struct TextGrid *tg, char *p) {
+    return (p - tg->data) % tg->cols;
+}
+unsigned TGrow(struct TextGrid *tg, char *p) {
+    return (p - tg->data) / tg->cols;
 }
 
 // TODO: rewrite this shit
 size_t linearize2d(unsigned width, unsigned row, unsigned col) {
     return (row * width) + col;

Index: aocutils.h
==================================================================
--- aocutils.h
+++ aocutils.h
@@ -8,10 +8,12 @@
     char *data; // may have '\n' at end of rows
 };
 
 bool TGvalid(struct TextGrid *tg, unsigned row, unsigned col);
 char *TGcharptr(struct TextGrid *tg, unsigned row, unsigned col);
+unsigned TGcol(struct TextGrid *tg, char *p);
+unsigned TGrow(struct TextGrid *tg, char *p);
 
 size_t linearize2d(unsigned width, unsigned row, unsigned col); // TODO
 size_t text2array(unsigned **dst, const char *txt);
 size_t slurp(char **dst, const char *filename);
 unsigned distance(unsigned a, unsigned b);