From 1f6d987c5391c5d71ec58d5391c2045700d23d87 Mon Sep 17 00:00:00 2001
From: Joseph Montanaro <jfmonty2@gmail.com>
Date: Mon, 2 Dec 2024 09:58:45 -0500
Subject: [PATCH] add 2024 day 1

---
 .gitignore |  2 ++
 2024/01.c  | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 81 insertions(+)
 create mode 100644 2024/01.c

diff --git a/.gitignore b/.gitignore
index 046a5d8..90f8ec7 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,5 @@
 */data/*
 */target/*
 **.exe
+
+*.out
diff --git a/2024/01.c b/2024/01.c
new file mode 100644
index 0000000..8ced499
--- /dev/null
+++ b/2024/01.c
@@ -0,0 +1,79 @@
+#include "stdio.h"
+#include "stdlib.h"
+#include "string.h"
+
+
+int cmp(const void *a, const void *b) {
+    int *_a = (int *)a;
+    int *_b = (int *)b;
+    return *_a - *_b;
+}
+
+
+int count_occurrences(int num, int arr[], int len) {
+    int total = 0;
+    for (int i = 0; i < len; i++) {
+        if (arr[i] == num) {
+            total++;
+        }
+    }
+    return total;
+}
+
+
+int part1(int nums_l[], int nums_r[], int len) {
+    int sum = 0;
+    for (int i = 0; i < len; i++) {
+        int diff = nums_l[i] - nums_r[i];
+        if (diff < 0) {
+            diff = diff * -1;
+        }
+        sum += diff;
+    }
+    return sum;
+}
+
+
+int part2(int nums_l[], int nums_r[], int len) {
+    int score = 0;
+    for (int i = 0; i < len; i++) {
+        score += nums_l[i] * count_occurrences(nums_l[i], nums_r, len);
+    }
+    return score;
+}
+
+
+int main() {
+    FILE *file = fopen("data/01.txt", "r");
+    char *data = (char *)malloc(16384);
+    size_t data_len = fread(data, 1, 16384, file);
+
+    int nums_l[1000];
+    int nums_r[1000];
+
+    int nlines = 0;
+    while (1) {
+        char* line = strsep(&data, "\n");
+        int left = strtol(line, &line, 10);
+        int right = strtol(line, NULL, 10);
+
+        // if `strtol` fails, it apparently just returns 0, how helpful
+        if (left == 0 && right == 0) {
+            break;
+        }
+
+        nums_l[nlines] = left;
+        nums_r[nlines] = right;
+
+        nlines++;
+    }
+
+    qsort(nums_l, nlines, 4, cmp);
+    qsort(nums_r, nlines, 4, cmp);
+
+    int solution_1 = part1(nums_l, nums_r, nlines);
+    printf("Part 1: %i\n", solution_1);
+
+    int solution_2 = part2(nums_l, nums_r, nlines);
+    printf("Part 2: %i\n", solution_2);
+}