day5p1

day5p1/Makefile

@@ -0,0 +1,8 @@
+CFLAGS := -Wall -Wextra -std=c17 -D_GNU_SOURCE
+
+.PHONY: all
+all: main
+
+.PHONY: clean
+clean:
+	rm -f main

day5p1/main.c

@@ -0,0 +1,91 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <ctype.h>
+
+void *read_file_contents(const char *fname, size_t *len)
+{
+    FILE *f = fopen(fname, "r");
+    if (!f) {
+        perror(fname);
+        return NULL;
+    }
+    fseek(f, 0, SEEK_END);
+    *len = ftell(f);
+    rewind(f);
+    void *contents = malloc(*len);
+    if (!contents) {
+        perror("malloc");
+        fclose(f);
+        return NULL;
+    }
+    fread(contents, *len, 1, f);
+    fclose(f);
+    return contents;
+}
+
+void remove_dupes(char *mem, size_t len)
+{
+    int found;
+    char last_char;
+    size_t last_char_pos;
+
+    do {
+        found = 0;
+        last_char = '\0';
+        last_char_pos = 0;
+
+        for (size_t i = 0; i < len; i++) {
+            if (!mem[i]) continue;
+
+            if (tolower(mem[i]) == tolower(last_char) &&
+                    mem[i] != last_char) {
+                mem[i] = mem[last_char_pos] = '\0';
+                found = 1;
+                last_char_pos = 0;
+                last_char = '\0';
+            } else {
+                last_char_pos = i;
+                last_char = mem[last_char_pos];
+            }
+        }
+    } while (found);
+}
+
+size_t strip_zeroes(char *mem, size_t len)
+{
+    size_t new_len = len;
+
+    char *current = mem + len - 1;
+    while (len) {
+        while (len && *current) {len--; current--;}
+        if (!len) break;
+
+        char *start = current;
+        while (len && !*current) {len--; current--;}
+        size_t diff = new_len - len - (start - current);
+        memmove(current + 1, start + 1, diff);
+        new_len = len + diff;
+    }
+
+    return new_len;
+}
+
+int main()
+{
+    size_t string_len;
+    char *string = read_file_contents("input", &string_len);
+    if (!string) return 0;
+
+    while (isspace(string[string_len - 1])) string[--string_len] = '\0';
+
+    puts("Removing dupes...");
+    remove_dupes(string, string_len);
+
+    puts("Stripping zeroes...");
+    string_len = strip_zeroes(string, string_len);
+    printf("Remaining polymers: %lu\n", string_len);
+
+    free(string);
+    return 0;
+}