rename repo, subdir for yearly challenges

2020/day13/ex2-c.c

@@ -0,0 +1,47 @@
+/* ex1-c: Advent2020 game, day 13/game 2
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+int main(ac, av)
+    int ac;
+    char **av;
+{
+    struct bus {
+        unsigned bus;
+        unsigned idx;
+    } buses[1024];
+    unsigned len=0, i=0, bus, idx;
+
+    char line[1024], *ptr=line;
+    unsigned long long lcm=1, result=0;
+
+    fgets(line, sizeof line, stdin);
+    fgets(line, sizeof line, stdin);
+    ptr=strtok(line, ",");
+
+    do {
+        if (*ptr != 'x') {
+            buses[len].bus=atol(ptr);
+            buses[len].idx=i;
+            len++;
+        }
+        i++;
+        ptr=strtok(NULL, ",");
+    } while (ptr);
+
+
+    for (i=0; i<len-1; ++i) {
+        bus=buses[i+1].bus;
+        idx=buses[i+1].idx;
+        lcm*=buses[i].bus;
+        while ((result+idx)%bus != 0) {
+            result+=lcm;
+        }
+    }
+
+    printf("%s : res=%llu\n", *av, result);
+    exit (0);
+}