From 1d96c68c66ba5648d1dd4d8ff2976fc97eea8a14 Mon Sep 17 00:00:00 2001
From: kartofen <mladenovnasko0@gmail.com>
Date: Sun, 31 Jul 2022 20:12:50 +0300
Subject: 2020 days 4 and 5

---
 Advent-of-Code-2020/AOC-5/main.c | 137 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 137 insertions(+)
 create mode 100644 Advent-of-Code-2020/AOC-5/main.c

(limited to 'Advent-of-Code-2020/AOC-5/main.c')

diff --git a/Advent-of-Code-2020/AOC-5/main.c b/Advent-of-Code-2020/AOC-5/main.c
new file mode 100644
index 0000000..2634753
--- /dev/null
+++ b/Advent-of-Code-2020/AOC-5/main.c
@@ -0,0 +1,137 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <assert.h>
+
+#if 0
+#define PART_1
+#else
+#define PART_2
+#endif
+
+#if 0
+#define FILE_PATH "example.txt"
+#define IDS 4
+#else
+#define FILE_PATH "input.txt"
+#define IDS 908
+#endif
+
+#define LOWER(min, max) ((max) - (((max) - (min))/2 + 1))
+#define UPPER(min, max) (((min) + (max))/2 + 1)
+
+#define ROWS  128
+#define COLUMNS 8
+
+int highest_id = 0;
+int ids[IDS] = {0};
+
+void process_pass(char *pass, int index)
+{
+    int min_r = 0; int max_r = ROWS - 1;
+    int min_c = 0; int max_c = COLUMNS - 1;
+
+    for(int i = 0; i < 10; i++)
+    {
+        switch(pass[i])
+        {
+        case 'F':
+            max_r = LOWER(min_r, max_r);
+            break;
+        case 'B':
+            min_r = UPPER(min_r, max_r);
+            break;
+        case 'L':
+            max_c = LOWER(min_c, max_c);
+            break;
+        case 'R':
+            min_c = UPPER(min_c, max_c);
+            break;
+        }
+    }
+
+    int id = min_r * 8 + min_c;
+
+#ifdef PART_1
+    (void)index;
+    if(id > highest_id) highest_id = id;
+#endif
+
+#ifdef PART_2
+    assert(index < IDS);
+    ids[index] = id;
+#endif
+
+}
+
+void parse()
+{
+    FILE *fp = fopen(FILE_PATH, "r");
+    if(!fp) {
+        fprintf(stderr, "ERROR: Could not open file: %s\n", FILE_PATH);
+        exit(EXIT_FAILURE);
+    }
+
+    int i = 0;
+    char line[256] = {0};
+    while(fgets(line, sizeof(line), fp) != NULL)
+    {
+        if(line[10] == '\n') line[10] = '\0';
+        process_pass(line, i);
+        i++;
+    }
+
+    fclose(fp);
+}
+
+int find_id()
+{
+    int your_seat;
+    int seat_missing;
+
+    for(int i = 0; i < IDS; i++)
+    {
+        your_seat    = -1;
+        seat_missing = 0;
+
+        for(int j = 0; j < IDS; j++)
+        {
+            if(ids[i] == (ids[j] + 2))
+            {
+                your_seat = ids[i] - 1;
+                seat_missing = 1;
+
+                for(int k = 0; k < IDS; k++)
+                    if(your_seat == ids[k]) seat_missing = 0;
+            }
+        }
+
+        if(your_seat!= -1 && seat_missing != 0)
+            return your_seat;
+
+    }
+    return -1;
+}
+
+void part_1()
+{
+    printf("Highest boarding ID is %d\n", highest_id);
+}
+
+void part_2()
+{
+    printf("Your id is: %d\n", find_id());
+}
+
+int main(void)
+{
+    parse();
+
+#ifdef PART_1
+    part_1();
+#endif
+#ifdef PART_2
+    part_2();
+#endif
+
+    return 0;
+}
-- 
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