Index: aoc2024.c
==================================================================
--- aoc2024.c
+++ aoc2024.c
@@ -29,10 +29,12 @@
     tg.data = data;
     tg.cols = strchr(data, '\n') - data + 1;
     tg.rows = tg.cols - 1; // rows includes the '\n'
     unsigned anti[512][2]; // locations of antinodes; col at index 0, row at 1
     unsigned nanti = 0;
+    unsigned anti2[1024][2]; // locations of antinodes; col at index 0, row at 1
+    unsigned nanti2 = 0;
 
     char *p = data;
     while (*p) {
         while ((*p == '.') || (*p == '\n')) p++;
         if (*p) {
@@ -42,34 +44,64 @@
             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;
+
                 int anticol = (int)pcol - deltacol;
                 int antirow = (int)prow - deltarow;
+                unsigned *ff;
                 if (TGvalid(&tg, (unsigned)anticol, (unsigned)antirow) && (*TGcharptr(&tg, (unsigned)anticol, (unsigned)antirow) != '\n')) {
-                    unsigned *ff = antinode_find(anti, nanti, (unsigned)anticol, (unsigned)antirow);
+                    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);
+                    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
+
+                int k;
+                // q - delta is p; q -2delta is one afterwards, etc
+                // add q - (k)delta to anti2 while valid
+                k = 1;
+                while (TGvalid(&tg, (unsigned)((int)qcol-k*deltacol), (unsigned)((int)qrow-k*deltarow)) && (*TGcharptr(&tg, (unsigned)((int)qcol-k*deltacol), (unsigned)((int)qrow-k*deltarow)) != '\n')) {
+                    ff = antinode_find(anti2, nanti2, (unsigned)((int)qcol-k*deltacol), (unsigned)((int)qrow-k*deltarow));
+                    if (!ff) {
+                        anti2[nanti2][0] = (unsigned)((int)qcol-k*deltacol);
+                        anti2[nanti2++][1] = (unsigned)((int)qrow-k*deltarow);
+                    }
+                    k++;
+                }
+                // p + delta is q; p +2delta is one afterwards, etc
+                // add p + (k)delta to anti2 while valid
+                k = 1;
+                while (TGvalid(&tg, (unsigned)((int)pcol+k*deltacol), (unsigned)((int)prow+k*deltarow)) && (*TGcharptr(&tg, (unsigned)((int)pcol+k*deltacol), (unsigned)((int)prow+k*deltarow)) != '\n')) {
+                    ff = antinode_find(anti2, nanti2, (unsigned)((int)pcol+k*deltacol), (unsigned)((int)prow+k*deltarow));
+                    if (!ff) {
+                        anti2[nanti2][0] = (unsigned)((int)pcol+k*deltacol);
+                        anti2[nanti2++][1] = (unsigned)((int)prow+k*deltarow);
+                    }
+                    k++;
+                }
+
+                // next antenna of this type
+                q = strchr(q+1, *p);
             }
             p += 1;
         }
     }
     printf("There are %u antinodes within the map.\n", nanti);
+    printf("There are %u resonant antinodes within the map.\n", nanti2);
 }
 
 /* === aoc202407 =======================================================
    Part one looks easy
    Part two also easy