09: Solve in C

09/solution.c

@@ -0,0 +1,83 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+
+typedef struct pos {
+    int32_t x;
+    int32_t y;
+    struct pos *next;
+} pos;
+
+#define TBL_CAP (0x01000193U+1)
+
+uint32_t fnv1a_32(pos p)
+{
+    uint32_t h = 0x01000193U * (0x811c9dc5U ^ p.x);
+    h = 0x01000193U * (h ^ p.y);
+
+    return h % TBL_CAP;
+}
+
+int tbl_get(pos **t, pos p) {
+    uint32_t idx = fnv1a_32(p);
+
+    pos *itm = t[idx];
+    if (!itm)
+        itm = t[idx] = calloc(1, sizeof(pos));
+    else if (itm->x != p.x || itm->y != p.y) {
+        for (;;) {
+            if (itm->next) {
+                if (itm->next->x == p.x && itm->next->y == p.y)
+                    return 0;
+                itm = itm->next;
+            } else {
+                itm = itm->next = calloc(1, sizeof(pos));
+                break;
+            }
+        }
+    } else return 0;
+
+    itm->x = p.x;
+    itm->y = p.y;
+
+    return 1;
+}
+
+int main(void) {
+    uint32_t S = 0, G = 0;
+    static pos *vS[TBL_CAP] = {0};
+    static pos *vG[TBL_CAP] = {0};
+    static pos rope[10] = {0};
+    char dir;
+    int steps;
+
+    while (scanf("%c %i\n", &dir, &steps) == 2) {
+        for (uint32_t s = 0; s < steps; s++) {
+            switch (dir) {
+                case 'U': rope[0].y++; break;
+                case 'D': rope[0].y--; break;
+                case 'L': rope[0].x--; break;
+                case 'R': rope[0].x++; break;
+            }
+
+            for (int r = 1; r < 10; r++) {
+                if (rope[r].x != rope[r-1].x || rope[r].y != rope[r-1].y) {
+                    int32_t hdiff = rope[r-1].x - rope[r].x;
+                    int32_t vdiff = rope[r-1].y - rope[r].y;
+                    int diag = abs(hdiff) + abs(vdiff) > 2;
+
+                    rope[r].x += (hdiff >  1 || (hdiff > 0 && diag));
+                    rope[r].x -= (hdiff < -1 || (hdiff < 0 && diag));
+                    rope[r].y += (vdiff >  1 || (vdiff > 0 && diag));
+                    rope[r].y -= (vdiff < -1 || (vdiff < 0 && diag));
+                }
+            }
+
+            S += tbl_get(vS, rope[1]);
+            G += tbl_get(vG, rope[9]);
+        }
+    }
+
+    printf("Silver: %u\nGold: %u\n", S, G);
+}