1 files changed, 135 insertions, 0 deletions
diff --git a/Advent-of-Code-2022/aoc-15/main.c b/Advent-of-Code-2022/aoc-15/main.c
new file mode 100644
index 0000000..242b150
--- /dev/null
+++ b/Advent-of-Code-2022/aoc-15/main.c
@@ -0,0 +1,135 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+
+#if 0
+  #define PART part1
+#else
+  #define PART part2
+#endif
+
+#if 0
+  #define FILENAME "sample.txt"
+  #define TARGET_Y 10
+  #define UPPER 20
+#else
+  #define FILENAME "input.txt"
+  #define TARGET_Y 2000000
+  #define UPPER 2000000
+#endif
+
+#define LOWER 1000000
+
+#define ENTRIES_CAP 30
+#define CAP 10000000
+#define OFFSET (CAP/2)
+
+int sensors[CAP][2];
+int beacons[CAP][2];
+size_t entries = 0;
+
+int obj[CAP];
+int row[CAP];
+
+size_t sum = 0;
+
+#define MAX(x, y) (((x) > (y)) ? (x) : (y))
+
+int taxi_distance(int x1, int y1, int x2, int y2)
+{
+    return abs(x1 - x2) + abs(y1 - y2);
+}
+
+void analyze(int target_y)
+{
+    memset(obj, 0, sizeof(obj));
+    memset(row, 0, sizeof(row));
+
+    for(size_t i = 0; i < entries; i++)
+    {
+        int x1 = sensors[i][0]; int x2 = beacons[i][0];
+        int y1 = sensors[i][1]; int y2 = beacons[i][1];
+
+        int r = taxi_distance(x1, y1, x2, y2);
+        int diff = abs(target_y - y1);
+        for(int i = x1 - (r - diff); i <= x1 + (r - diff); i++) {
+            row[i + OFFSET] = 1;
+        }
+
+        if(y2 == target_y) obj[x2 + OFFSET] = 1;
+    }
+}
+
+void part1()
+{
+    analyze(TARGET_Y);
+
+    for(size_t i = 0; i < CAP; i++)
+        if(row[i] - obj[i] > 0) sum++;
+}
+
+void part2()
+{
+    for(int y = LOWER; y <= UPPER; y++)
+    {
+        printf("%d\n", y);
+        analyze(y);
+
+        for(int x = LOWER; x <= UPPER; x++)
+            if(row[x + OFFSET] == 0 && obj[x + OFFSET] == 0) {
+                sum = (x * 4000000) + y;
+                return;
+            }
+    }
+
+    exit(1);
+}
+
+void parse_xy(char *str, int *x, int *y, int nth)
+{
+    char *s, *sx;
+    char *y_str, *x_str;
+
+    x_str = strtok_r(strtok_r(str, ",", &s), " ", &sx);
+    y_str = strtok_r(NULL, ",", &s);
+
+    for(int i = 1; i < nth; i++)
+        x_str = strtok_r(NULL, " ", &sx);
+
+    assert(x_str != NULL);
+    assert(y_str != NULL);
+
+    *x = atoi(&(x_str[2]));
+    *y = atoi(&(y_str[3]));
+}
+
+void parse()
+{
+    FILE *fp = fopen(FILENAME, "r");
+    if(!fp) {
+        fprintf(stderr, "ERROR: Could not open file: %s\n", FILENAME);
+        exit(1);
+    }
+
+    char line[512];
+    while(fgets(line, sizeof(line), fp))
+    {
+        size_t len = strlen(line);
+        if(line[len-1] == '\n') line[len-1] = 0;
+
+        parse_xy(strtok(line, ":"), &sensors[entries][0], &sensors[entries][1], 3);
+        parse_xy(strtok(NULL, ":"), &beacons[entries][0], &beacons[entries][1], 5);
+        entries++;
+    }
+
+    fclose(fp);
+}
+
+int main(void)
+{
+    parse();
+    PART();
+    printf("%ld\n", sum);
+    return 0;
+}