From 709005f9a565405d9413eebf8c4ccaff53f0654a Mon Sep 17 00:00:00 2001
From: Sebastiano Tronto <sebastiano@tronto.net>
Date: Fri, 22 Dec 2023 16:44:48 +0100
Subject: Added solutions for 21 and 22

---
 2023/21/21a.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)
 create mode 100644 2023/21/21a.c

(limited to '2023/21/21a.c')

diff --git a/2023/21/21a.c b/2023/21/21a.c
new file mode 100644
index 0000000..a4009d9
--- /dev/null
+++ b/2023/21/21a.c
@@ -0,0 +1,54 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define N 200
+
+typedef struct { int i, j; } point_t;
+
+char map[N][N];
+int n, nq, nnext;
+point_t s, q[N*N], nextq[N*N];
+
+bool bad(point_t p) {
+	int i = p.i, j = p.j;
+	return i < 0 || j < 0 || i >= n || j >= n || map[i][j] == '#';
+}
+
+void add(point_t p) {
+	if (bad(p)) return;
+	for (int i = 0; i < nnext; i++)
+		if (nextq[i].i == p.i && nextq[i].j == p.j)
+			return;
+	nextq[nnext++] = p;
+}
+
+point_t up(point_t p) { return (point_t) {.i = p.i-1, .j = p.j}; }
+point_t down(point_t p) { return (point_t) {.i = p.i+1, .j = p.j}; }
+point_t right(point_t p) { return (point_t) {.i = p.i, .j = p.j+1}; }
+point_t left(point_t p) { return (point_t) {.i = p.i, .j = p.j-1}; }
+
+int main() {
+	for (n = 0; fgets(map[n], N, stdin) != NULL; n++)
+		for (int i = 0; map[n][i] != '\n'; i++)
+			if (map[n][i] == 'S')
+				s = (point_t) {.i = n, .j = i};
+
+	int d = 64;
+	add(s);
+	for (int i = 0; i < d; i++) {
+		memcpy(q, nextq, nnext * sizeof(point_t));
+		nq = nnext;
+		nnext = 0;
+		for (int j = 0; j < nq; j++) {
+			add(up(q[j]));
+			add(down(q[j]));
+			add(right(q[j]));
+			add(left(q[j]));
+		}
+	}
+
+	printf("%d\n", nnext);
+	return 0;
+}
-- 
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