1 files changed, 176 insertions, 0 deletions
diff --git a/god_hands.c b/god_hands.c
new file mode 100644
index 0000000..4ff2f5d
--- /dev/null
+++ b/god_hands.c
@@ -0,0 +1,176 @@
+#include <stdint.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <assert.h>
+#include <stdbool.h>
+
+typedef uint8_t byte;
+typedef int8_t rang_t;
+
+typedef struct {
+    byte value;
+    rang_t rang;
+} elem_t;
+
+typedef struct {
+    int len;
+    elem_t *elem;
+} map_t;
+
+map_t *map_g;
+
+/* resolve {{{ */
+
+/* returns true if the map is empty, otherwise returns false */
+static bool map_is_empty(void)
+{
+    for (int i = 0; i < map_g->len; i++) {
+        if (map_g->elem[i].rang == -1) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
+/* return the index of the next element */
+static inline int get_next_case(int current)
+{
+    return (current + map_g->elem[current].value) % map_g->len;
+}
+
+/* return the index of the previous element */
+static inline int get_prev_case(int current)
+{
+    int prev = current - map_g->elem[current].value;
+
+    if (current < map_g->elem[current].value)
+        prev += map_g->len;
+
+    return prev;
+}
+
+static int perform_resolve_god_hands(int activated, int offset)
+{
+    int next, prev;
+
+    /* this one is already activated, not possible captain */
+    if (map_g->elem[activated].rang != -1) {
+        return -1;
+    }
+
+    /* activate the current case */
+    map_g->elem[activated].rang = offset;
+
+    if (map_is_empty()) {
+        /* we won */
+        return 0;
+    }
+
+    next = get_next_case(activated);
+    prev = get_prev_case(activated);
+
+    if (perform_resolve_god_hands(next, offset + 1) == 0)
+        return 0;
+
+    if (perform_resolve_god_hands(prev, offset + 1) == 0)
+        return 0;
+
+    /* reset to default */
+    map_g->elem[activated].rang = -1;
+    return -1;
+}
+
+int solve_god_hands(map_t *map)
+{
+    for (int i = 0; i < map->len; i++) {
+        map->elem[i].rang = -1;
+    }
+
+    map_g = map;
+
+    for (int i = 0; i < map->len; i++) {
+        if (perform_resolve_god_hands(i, 0) == 0) {
+            return 0;
+        }
+    }
+
+    return -1;
+}
+
+/* }}} */
+
+static void display_solution(const map_t *map)
+{
+    for (int i = 0; i < map->len; i++) {
+        /* run through the order */
+        for (int j = 0; j < map->len; j++) {
+            /* run through the elems */
+
+            assert (map->elem[j].rang != -1);
+
+            if (map->elem[j].rang == i) {
+                printf("[%d] ", j);
+                break;
+            }
+        }
+    }
+    putchar('\n');
+}
+
+int main(void)
+{
+    map_t map;
+    char buffer[16];
+
+    /* get the length of the map */
+    for (;;) {
+        if (isatty(STDIN_FILENO) && isatty(STDOUT_FILENO)) {
+            fputs("size of the map: ", stdout);
+        }
+
+        if (fgets(buffer, sizeof(buffer), stdin) == NULL) {
+            return 0;
+        }
+
+        /* TODO replace with strtol to handle errors of type 42(.*) */
+        map.len = atoi(buffer);
+
+        if (map.len <= 0) {
+            fprintf(stderr, "the map has an invalid size\n");
+
+            if (!isatty(STDIN_FILENO))
+                return -1;
+
+            continue;
+        }
+
+        break;
+    }
+
+    map.elem = malloc(sizeof(elem_t) * map.len);
+
+    for (int i = 0; i < map.len; i++) {
+        if (isatty(STDIN_FILENO) && isatty(STDOUT_FILENO))
+            printf("(%02d/%02d): ", i + 1, map.len);
+
+        fflush(stdout);
+
+        if (fgets(buffer, sizeof(buffer), stdin) == NULL) {
+            return 0;
+        }
+
+        /* TODO check for errors (i.e. not numbers and negative values */
+        map.elem[i].value = atoi(buffer);
+    }
+
+    if ((solve_god_hands(&map)) != 0) {
+        fputs("cannot solve the paradox, kupo :-/\n", stderr);
+    } else {
+        fputs("we solved the paradox kupo! :-)\n", stdout);
+        display_solution(&map);
+    }
+
+    return 0;
+}