Very beautiful and efficient

1 files changed, 121 insertions, 0 deletions

diff --git a/2021/04/solve.c b/2021/04/solve.c
new file mode 100644
index 0000000..b9b4096
--- /dev/null
+++ b/2021/04/solve.c
@@ -0,0 +1,121 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+
+typedef int board[5][5];
+
+// Very beautiful and efficient!!
+static int check_board(board input, int *numbers, int cnt)
+{
+	board marked = { 0 };
+
+	for (int i = 0; i < cnt; i++) {
+		for (int y = 0; y < 5; y++) {
+			for (int x = 0; x < 5; x++) {
+				if (input[y][x] == numbers[i]) {
+					marked[y][x] = 1;
+					break;
+				}
+			}
+		}
+	}
+
+	for (int y = 0; y < 5; y++) {
+		int row = 0;
+		for (int x = 0; x < 5; x++) {
+			if (marked[y][x])
+				row++;
+		}
+		if (row == 5)
+			goto bingo;
+	}
+
+	for (int x = 0; x < 5; x++) {
+		int column = 0;
+		for (int y = 0; y < 5; y++) {
+			if (marked[y][x])
+				column++;
+		}
+		if (column == 5)
+			goto bingo;
+	}
+
+	return 0;
+
+bingo:;
+	int res = 0;
+	for (int x = 0; x < 5; x++) {
+		for (int y = 0; y < 5; y++) {
+			if (!marked[y][x])
+				res += input[y][x];
+		}
+	}
+	return res;
+}
+
+static void solve(FILE *fp)
+{
+	int numbers[256] = { 0 };
+	int cnt = 0;
+	char ch = 0;
+	while (fscanf(fp, "%d%c", &numbers[cnt], &ch) > 0 && ch == ',')
+		cnt++;
+
+	board boards[256];
+	memset(boards, 0xffff, sizeof(board) * 256);
+
+	int board_cnt = 0;
+	int x = 0, y = 0;
+	while (1) {
+		if (fscanf(fp, "%d%c", &boards[board_cnt][x][y], &ch) < 1)
+			break;
+
+		if (x++ == 4) {
+			y++;
+			x = 0;
+		}
+		if (y == 5) {
+			board_cnt++;
+			x = 0;
+			y = 0;
+		}
+	}
+
+	int won = 0;
+	for (int num = 0; num < cnt; num++) {
+		for (int i = 0; i < board_cnt; i++) {
+			if (boards[i][0][0] == 0x424242)
+				continue;
+
+			int bingo = 0;
+			if ((bingo = check_board(boards[i], numbers, num + 1))) {
+				boards[i][0][0] = 0x424242;
+				won++;
+
+				if (won == 1 || won == board_cnt)
+					printf("%d\n", bingo * numbers[num]);
+				if (won == board_cnt)
+					return;
+			}
+		}
+	}
+}
+
+int main(int argc, char *argv[])
+{
+	(void)argc;
+	(void)argv;
+
+	FILE *fp = fopen("input", "r");
+	if (!fp)
+		exit(EXIT_FAILURE);
+
+	clock_t tic = clock();
+	solve(fp);
+	clock_t toc = clock();
+	printf("TIME: %f seconds\n", (double)(toc - tic) / CLOCKS_PER_SEC);
+
+	fclose(fp);
+	return 0;
+}