1 files changed, 127 insertions, 0 deletions
diff --git a/01/b.c b/01/b.c
new file mode 100644
index 0000000..773ab73
--- /dev/null
+++ b/01/b.c
@@ -0,0 +1,127 @@
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#define BUF_SIZE 2000
+
+char buf[BUF_SIZE];
+int input[200];
+int length;
+
+void read_input() {
+    int fd = open("input.txt", O_RDONLY);
+    ssize_t bytes_read = read(fd, buf, BUF_SIZE-1);
+    if (bytes_read <= 0) {
+        printf("Error reading input\n");
+        exit(1);
+    }
+    buf[bytes_read] = '\0';
+}
+
+void parse_input() {
+    int offset = 0;
+    int done = 0;
+    int buf_offset = 0;
+    int i = 0;
+    char current[10];
+
+    while (!done) {
+        int current_offset = 0;
+        while (buf[buf_offset] != '\n' && buf[buf_offset] != '\0') {
+            current[current_offset++] = buf[buf_offset++];
+        }
+        if (buf[buf_offset] == '\0') {
+            done = 1;
+        } else {
+            buf_offset++;
+            current[current_offset] = '\0';
+            input[i++] = atoi(current);
+            length = i;
+        }
+    }
+}
+
+int int_less(const void *a, const void *b) {
+    return *(int *)a - *(int *)b;
+}
+
+void sort_input() {
+    qsort(input, length, sizeof(int), int_less);
+}
+
+int bin_search(int small_pointer, int large_pointer) {
+    int small = input[small_pointer];
+    int big = input[large_pointer];
+    int mid = (large_pointer + small_pointer) / 2;
+    int sum = small + big + input[mid];
+    while (sum != 2020 && small_pointer < large_pointer) {
+        if (sum > 2020) {
+            large_pointer = mid - 1;
+            mid = (large_pointer + small_pointer) / 2;
+        } else {
+            small_pointer = mid + 1;
+            mid = (large_pointer + small_pointer) / 2;
+        }
+        sum = small + big + input[mid];
+    }
+
+    if (sum == 2020) {
+        return mid;
+    } else {
+        return -1;
+    }
+}
+
+int search_2020() {
+    int small_pointer = 0;
+    int large_pointer = length - 1;
+    int sum_small = input[small_pointer] + input[small_pointer + 1] + input[large_pointer];
+    int sum_large = input[small_pointer] + input[large_pointer] + input[large_pointer - 1];
+    int done = 0;
+    int mid;
+    while (sum_large != 2020 && sum_small != 2020 && small_pointer + 1 != large_pointer && !done) {
+        if (sum_small > 2020) {
+            large_pointer--;
+        } else if (sum_large < 2020) {
+            small_pointer++;
+        } else {
+            mid = bin_search(small_pointer, large_pointer);
+            if (mid > 0) {
+                done = 1;
+            } else {
+                mid = bin_search(small_pointer + 1, large_pointer);
+                if (mid > 0) {
+                    done = 1;
+                } else {
+                    mid = bin_search(small_pointer, large_pointer - 1);
+                    if (mid > 0) {
+                        done = 1;
+                    } else {
+                        small_pointer++;
+                        large_pointer--;
+                    }
+                }
+            }
+        }
+
+        sum_small = input[small_pointer] + input[small_pointer + 1] + input[large_pointer];
+        sum_large = input[small_pointer] + input[large_pointer] + input[large_pointer - 1];
+    }
+    return input[small_pointer] * input[large_pointer] * input[mid];
+}
+
+void print_input() {
+    for (int i = 0; i < length; i++) {
+        printf("%d\n", input[i]);
+    }
+}
+
+int main() {
+    read_input();
+    parse_input(); 
+    sort_input();
+    printf("%d\n", search_2020());
+}
+