Added solution for 23

2 files changed, 135 insertions, 0 deletions

diff --git a/2023/23/23a.c b/2023/23/23a.c
new file mode 100644
index 0000000..fb6ac7d
--- /dev/null
+++ b/2023/23/23a.c
@@ -0,0 +1,38 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define N 200
+
+bool v[N][N];
+char map[N][N];
+int n, s, t, sol;
+
+int max(int x, int y) { return x > y ? x : y; }
+
+int longpath(int i, int j) {
+        if (i == n-1 && j == t) return 0;
+        if (v[i][j]) return -1;
+
+        char c = map[i][j];
+        int ret = -1;
+        v[i][j] = true;
+        if (c == '.' || c == '>') ret = max(ret, longpath(i, j+1));
+        if (c == '.' || c == 'v') ret = max(ret, longpath(i+1, j));
+        if (c == '.' || c == '<') ret = max(ret, longpath(i, j-1));
+        if (c == '.' || c == '^') ret = max(ret, longpath(i-1, j));
+        v[i][j] = false;
+
+        return ret == -1 ? ret : ret + 1;
+}
+
+int main() {
+        for (n = 1; fgets(map[n], N, stdin) != NULL; n++) ;
+        memset(map[0], '#', n);
+        for (int i = 0; i < n; i++) if (map[1][i] == '.') s = i;
+        for (int i = 0; i < n; i++) if (map[n-1][i] == '.') t = i;
+
+        printf("%d\n", longpath(1, s));
+        return 0;
+}
diff --git a/2023/23/23b.c b/2023/23/23b.c
new file mode 100644
index 0000000..9635805
--- /dev/null
+++ b/2023/23/23b.c
@@ -0,0 +1,97 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define N 150
+#define V 1000
+
+typedef struct { int i, j; } node_t;
+typedef struct { int u, w; } edge_t;
+int d[4][2] = {{1, 0}, {-1, 0}, {0, 1}, {0, -1}};
+
+bool v[N][N];
+char map[N][N];
+int n, s, t, nv, ne[V];
+node_t node[V];
+edge_t g[V][4];
+
+int max(int x, int y) { return x > y ? x : y; }
+
+bool isjunc(int i, int j) {
+        int nn = 0;
+        for (int k = 0; k < 4; k++)
+                nn += map[i+d[k][0]][j+d[k][1]] == '#';
+        return nn != 2;
+}
+
+void advance(int io, int jo, int *i, int *j) {
+        for (int k = 0; k < 4; k++) {
+                int ni = *i + d[k][0], nj = *j + d[k][1];
+                if (!v[ni][nj] && (ni != io || nj != jo) &&
+                    map[ni][nj] != '#') {
+                        *i = ni;
+                        *j = nj;
+                        if (!isjunc(*i, *j)) v[*i][*j] = true;
+                        return;
+                }
+        }
+}
+
+int findorcreate(int i, int j) {
+        for (int u = 0; u < nv; u++)
+                if (node[u].i == i && node[u].j == j)
+                        return u;
+        node[nv] = (node_t) {.i = i, .j = j};
+        return nv++;
+}
+
+edge_t findedge(int io, int jo, int i, int j) {
+        int w;
+        v[i][j] = true;
+        for (w = 1; !isjunc(i, j); w++) advance(io, jo, &i, &j);
+        return (edge_t) {.u = findorcreate(i, j), .w = w};
+}
+
+void makegraph(int u) {
+        int i = node[u].i, j = node[u].j;
+        for (int k = 0; k < 4; k++) {
+                int ni = i + d[k][0], nj = j + d[k][1];
+                if (!v[ni][nj] && map[ni][nj] != '#') {
+                        edge_t e = findedge(i, j, ni, nj);
+                        g[u][ne[u]++] = (edge_t) {.u = e.u, .w = e.w};
+                        g[e.u][ne[e.u]++] = (edge_t) {.u = u, .w = e.w};
+                }
+        }
+}
+
+int longpath(int u) {
+        int i = node[u].i, j = node[u].j, k, ret, p;
+
+        if (i == n-1 && j == t) return 0;
+        if (v[i][j]) return -1;
+
+        v[i][j] = true;
+        for (ret = -1, k = 0; k < ne[u]; k++)
+                if ((p = longpath(g[u][k].u)) != -1)
+                        ret = max(ret, g[u][k].w + p);
+        v[i][j] = false;
+
+        return ret;
+}
+
+int main() {
+        for (n = 1; fgets(map[n], N, stdin) != NULL; n++) ;
+        memset(map[0], '#', n);
+        memset(map[n], '#', n);
+        for (int i = 0; i < n; i++) if (map[1][i] == '.') s = i;
+        for (int i = 0; i < n; i++) if (map[n-1][i] == '.') t = i;
+
+        findorcreate(1, s);
+        for (int u = 0; u < nv; u++)
+                makegraph(u);
+
+        printf("%d\n", longpath(0));
+
+        return 0;
+}