day 01

day-01/main.c

@@ -0,0 +1,56 @@
+#include "aoc.h"
+#include <stdlib.h>
+
+typedef struct {
+    i64 *data;
+    isize len, cap;
+} Ints;
+
+static int
+cmp_i64(const void *a, const void *b) {
+    return *(i64 *)a - *(i64 *)b;
+}
+
+int main(int argc, char **argv) {
+    Arena *arena = make_arena(Megabytes(1));
+    Arena *temp = make_arena(Megabytes(1));
+
+    Ints left = {0}, right = {0};
+
+    Tokens lines = read_lines(arena, argv[1]);
+    for (isize i = 0; i < lines.len; i++) {
+        str line = lines.tokens[i];
+        str fst, snd;
+        str_split(line, STR(" "), &fst, &snd);
+
+        *push(&left, arena)  = parse_i64(str_trim(fst), *temp);
+        *push(&right, arena) = parse_i64(str_trim(snd), *temp);
+    }
+
+    // Part 1
+    qsort(left.data, left.len, sizeof(i64), cmp_i64);
+    qsort(right.data, right.len, sizeof(i64), cmp_i64);
+
+    i64 part_1 = 0;
+    ASSERT(left.len == right.len);
+    for (isize i = 0; i < left.len; i++) {
+        part_1 += labs(left.data[i] - right.data[i]);
+    }
+    printf("%ld\n", part_1);
+    ASSERT(part_1 == 1223326);
+
+    // Part 2
+    i64 part_2 = 0;
+    for (isize i = 0; i < left.len; i++) {
+        i64 l = left.data[i], r = right.data[i];
+        // count occurrences of `l` in `right`
+        int occurrences = 0;
+        // since arrays are sorted, only need to go up to value `l`
+        for (isize j = 0; j < right.len && right.data[j] <= l; j++) {
+            occurrences += (right.data[j] == l);
+        }
+        part_2 += l * occurrences;
+    }
+    printf("%ld\n", part_2);
+    ASSERT(part_2 == 21070419);
+}

day-01/test.txt

@@ -0,0 +1,6 @@
+3   4
+4   3
+2   5
+1   3
+3   9
+3   3