Index: Makefile
==================================================================
--- Makefile
+++ Makefile
@@ -1,6 +1,6 @@
-all: aoc aocdbg aocclang aoctcc
+all: aocdbg aoc aocclang aoctcc
 
 clean:
 	rm aocdbg aoc aocclang aoctcc
 
 aocdbg: *.c *.h

Index: aoc2024.c
==================================================================
--- aoc2024.c
+++ aoc2024.c
@@ -12,21 +12,27 @@
    Idea: for all points p with an antenna find all points q>p with
 a corresponding frequency. For each such pair calculate the 2 antinodes
 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
 ===================================================================== */
+
+static unsigned *antinode_find(unsigned (*a)[2], size_t n,
+                               unsigned col, unsigned row) {
+    for (size_t k = 0; k < n; k++) {
+        if ((a[k][0] == col) && (a[k][1] == row)) return a[k];
+    }
+    return NULL;
+}
 
 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 anti[512][2]; // locations of antinodes; col at index 0, row at 1
     unsigned nanti = 0;
-    #endif
 
     char *p = data;
     while (*p) {
         while ((*p == '.') || (*p == '\n')) p++;
         if (*p) {
@@ -36,56 +42,34 @@
             while (q) {
                 // q points to an antenna of the same type as p
                 unsigned qrow = TGrow(&tg, q), qcol = TGcol(&tg, q);
                 int deltarow = (int)qrow - (int)prow;
                 int deltacol = (int)qcol - (int)pcol;
-                printf("p is at (C:%u, R:%u); q is at (C:%u, R:%u) ... delta: (C: %d, R: %d)\n",
-                      pcol, prow, qcol, qrow, deltacol, deltarow);
-                int col1 = (int)pcol - deltacol, row1 = (int)prow - deltarow;
-                if (TGvalid(&tg, row1, col1)) {
-                    printf("antinode at (C:%u, R:%u)\n", col1, row1);
-                }
-                int col2 = (int)qcol + deltacol, row2 = (int)qrow + deltarow;
-                if (TGvalid(&tg, row2, col2)) {
-                    printf("antinode at (C:%u, R:%u)\n", col2, row2);
+                int anticol = (int)pcol - deltacol;
+                int antirow = (int)prow - deltarow;
+                if (TGvalid(&tg, (unsigned)anticol, (unsigned)antirow) && (*TGcharptr(&tg, (unsigned)anticol, (unsigned)antirow) != '\n')) {
+                    unsigned *ff = antinode_find(anti, nanti, (unsigned)anticol, (unsigned)antirow);
+                    if (!ff) {
+                        anti[nanti][0] = (unsigned)anticol;
+                        anti[nanti++][1] = (unsigned)antirow;
+                    }
+                }
+                anticol = (int)qcol + deltacol;
+                antirow = (int)qrow + deltarow;
+                if (TGvalid(&tg, (unsigned)anticol, (unsigned)antirow) && (*TGcharptr(&tg, (unsigned)anticol, (unsigned)antirow) != '\n')) {
+                    unsigned *ff = antinode_find(anti, nanti, (unsigned)anticol, (unsigned)antirow);
+                    if (!ff) {
+                        anti[nanti][0] = (unsigned)anticol;
+                        anti[nanti++][1] = (unsigned)antirow;
+                    }
                 }
                 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 != '.') {
-                char *q = strchr(p + 1, *p);
-                while (q) {
-                    printf("found '%c'('%c')\n", *p, *q);
-                    ptrdiff_t delta = q - p;
-#if 0
-                    int row_pos = (int)(linear_pos / size);
-                    int col_pos = (int)(linear_pos % size);
-#endif
-                    if (p >= data + delta) {
-                        // antinode
-                        anti[nanti][0] = row(p - delta);
-                        anti[nanti++][1] = col(p - delta);
-                    }
-                    if (q < "end of data" - delta) {
-                        // antinode
-                        anti[nanti][0] = row(q + delta);
-                        anti[nanti++][1] = col(q + delta);
-                    }
-                    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

Index: aocutils.c
==================================================================
--- aocutils.c
+++ aocutils.c
@@ -1,17 +1,17 @@
 #include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include "aocutils.h"
 
-bool TGvalid(struct TextGrid *tg, unsigned row, unsigned col) {
+bool TGvalid(struct TextGrid *tg, unsigned col, unsigned row) {
     if (row >= tg->rows) return false;
     if (col >= tg->cols) return false;
     return true;
 }
-char *TGcharptr(struct TextGrid *tg, unsigned row, unsigned col) {
-    if (!TGvalid(tg, row, col)) return NULL;
+char *TGcharptr(struct TextGrid *tg, unsigned col, unsigned row) {
+    if (!TGvalid(tg, col, row)) return NULL;
     return tg->data + (row * tg->cols) + col;
 }
 unsigned TGcol(struct TextGrid *tg, char *p) {
     return (p - tg->data) % tg->cols;
 }

Index: aocutils.h
==================================================================
--- aocutils.h
+++ aocutils.h
@@ -2,16 +2,16 @@
 #define AOCUTILS_H_INCLUDED
 
 #include <stdbool.h>
 
 struct TextGrid {
-    unsigned rows, cols;
+    unsigned cols, rows;
     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);
+bool TGvalid(struct TextGrid *tg, unsigned col, unsigned row);
+char *TGcharptr(struct TextGrid *tg, unsigned col, unsigned row);
 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);