day 18

[advent21.git] / 18a.c

diff --git a/18a.c b/18a.c
index 719c3f0..acec8d3 100644 (file)
--- a/18a.c
+++ b/18a.c
@@ -4,52 +4,149 @@
 #include <ctype.h>
 
 struct number {
-       int depth;
        int number;
+       int depth;
+       struct number *prev;
+       struct number *next;
 };
 
-int parse_number(struct number numbers[])
+void print_number(struct number *head)
+{
+       for (struct number *e = head; e != NULL; e = e->next)
+               printf("(%d,%d) ", e->number, e->depth);
+       printf("\n");
+}
+
+struct number *parse_comp(struct number *prev, int *depth)
 {
-       int ns = 0;
-       int depth = 0;
        int c = getchar();
-       while ((c = getchar()) != '\n') {
-               switch(c) {
-               case '[':
-                       depth++;
-                       break;
-               case ']':
-                       depth--;
-                       break;
-               case ',':
-                       break;
-               default:
-                       if (isdigit(c))
-                               numbers[ns++] = (struct number){.depth=depth, .number=c-'0'};
-                       else
-                               printf("halp\n");
-                       break;
-               }
+       if (isdigit(c)) {
+               struct number *r = malloc(sizeof(struct number));
+               r->next = NULL;
+               r->prev = prev;
+               if (prev != NULL)
+                       prev->next = r;
+               r->number = c-'0';
+               r->depth = *depth;
+               return r;
+       } else if (c == ',') {
+               return parse_comp(prev, depth);
+       } else if (c == '[') {
+               *depth = *depth+1;
+               return parse_comp(prev, depth);
+       } else if (c == ']') {
+               *depth = *depth-1;
+               return parse_comp(prev, depth);
+       } else if (c != '\n' && c != EOF) {
+               printf("unknown character: '%c': %d\n", c, c);
        }
-       return ns;
+       return NULL;
 }
 
-void print_number(struct number n[], int ns)
+struct number *parse_number()
 {
-       int olddepth = 0;
-       for (int i = 0; i<ns; i++) {
-               if (n[i].depth > olddepth)
-                       printf("[");
-               else if (n[i].depth < olddepth)
-                       printf("]");
-               printf("%d ", n[i].number);
-               olddepth = n[i].depth;
+       int depth = 0;
+       struct number *head = parse_comp(NULL, &depth);
+       if (head == NULL)
+               return NULL;
+       struct number *e = head;
+       while ((e = parse_comp(e, &depth)) != NULL)
+               ;
+       return head;
+}
+
+void add_number(struct number *sum, struct number *oper)
+{
+       //increase depth of sum
+       struct number *e = sum;
+       for (; e->next != NULL; e = e->next)
+               e->depth++;
+       //append
+       e->next = oper;
+       oper->prev = e;
+       //increase depth of oper
+       for (; e != NULL; e = e->next)
+               e->depth++;
+}
+
+bool explode_number(struct number *e)
+{
+       if (e->depth <= 4)
+               return false;
+       struct number *l = e;
+       struct number *r = e->next;
+       if (l->prev != NULL)
+               l->prev->number += l->number;
+       if (r->next != NULL)
+               r->next->number += r->number;
+       l->number = 0;
+       l->depth--;
+       l->next = r->next;
+       if (l->next != NULL)
+               l->next->prev = l;
+       if (l->prev != NULL)
+               e = l->prev;
+       free(r);
+       return true;
+}
+
+bool split_number(struct number *e)
+{
+       if (e->number < 10)
+               return false;
+       struct number *i = malloc(sizeof(struct number));
+       i->number = e->number/2 + (e->number%2);
+       i->depth = e->depth+1;
+       i->prev = e;
+       i->next = e->next;
+       e->next = i;
+       e->number = e->number/2;
+       e->depth = e->depth+1;
+       return true;
+}
+
+void reduce_number(struct number *n)
+{
+       bool appliedaction;
+       do {
+               appliedaction = false;
+               for (struct number *e = n; e != NULL && !appliedaction; e = e->next)
+                       appliedaction |= explode_number(e);
+               for (struct number *e = n; e != NULL && !appliedaction; e = e->next)
+                       appliedaction |= split_number(e);
+       } while (appliedaction);
+}
+
+int magnitude_number(struct number *n)
+{
+       int maxdepth = 4;
+       while (n->next != NULL) {
+               for (struct number *e = n; e != NULL; e = e->next) {
+                       if (e->depth == maxdepth) {
+                               struct number *l = e;
+                               struct number *r = e->next;
+                               l->depth--;
+                               l->number = l->number*3 + r->number*2;
+                               l->next = r->next;
+                               if (r->next != NULL)
+                                       r->next->prev = l;
+                               free(r);
+                       }
+               }
+               maxdepth--;
        }
+       int r = n->number;
+       free(n);
+       return r;
 }
 
 int main ()
 {
-       struct number n[100];
-       int ns = parse_number(n);
-       print_number(n, ns);
+       struct number *sum = parse_number();
+       struct number *oper;
+       while ((oper = parse_number()) != NULL) {
+               add_number(sum, oper);
+               reduce_number(sum);
+       }
+       printf("%d\n", magnitude_number(sum));
 }