1 files changed, 92 insertions, 0 deletions

diff --git a/2023/18/18b.c b/2023/18/18b.c
new file mode 100644
index 0000000..d79d4cb
--- /dev/null
+++ b/2023/18/18b.c
@@ -0,0 +1,92 @@
+/*
+I have lost my code for part one. It reused some stuff from day 10.
+This code can be adjusted to work for part one, just change the input reading.
+*/
+
+#include <inttypes.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define N 1000
+#define MAX(x,y) ((x)>(y)?(x):(y))
+#define MIN(x,y) ((x)<(y)?(x):(y))
+
+typedef struct { int64_t i, j; } point_t;
+
+char *buf, in[50];
+int64_t k, l, oldl, n, r, t, nolda, nb, a[N], olda[N], b[N];
+point_t p[N];
+point_t go[] = {{.i=0, .j=1}, {.i=1, .j=0}, {.i=0, .j=-1}, {.i=-1, .j=0}};
+
+int cmp_int64(const void *x, const void *y) {
+        const int64_t *a = x, *b = y;
+        return *a > *b ? 1 : (*a < *b) ? -1 : 0;
+}
+
+int cmp_point(const void *x, const void *y) {
+        const point_t *p = x, *q = y;
+        int a = cmp_int64(&p->i, &q->i);
+        int b = cmp_int64(&p->j, &q->j);
+        return a ? a : b;
+}
+
+int64_t val(char c) {
+        if (c >= '0' && c <= '9') return c - '0';
+        return c - 'a' + 10;
+}
+
+int64_t removedoubles(int64_t a[], int64_t n) {
+        int64_t i, j = 0;
+        for (i = 0; i < n; i++) {
+                a[j] = a[i];
+                if (i+1 < n && a[j] == a[i+1])
+                        i++;
+                else
+                        j++;
+        }
+        return j;
+}
+
+int64_t overlaplen(int64_t a[], int64_t na, int64_t b[], int64_t nb) {
+        int64_t ret = 0;
+        for (int64_t i = 0; 2*i+1 < na; i++)
+                for (int64_t j = 0; 2*j+1 < nb; j++)
+                        ret += MAX(0,
+                            MIN(a[2*i+1], b[2*j+1]) - MAX(a[2*i], b[2*j]) + 1);
+        return ret;
+}
+
+int64_t linelen(int64_t a[], int64_t n) {
+        return overlaplen(a, n, a, n);
+}
+
+int main() {
+        p[n++] = (point_t) {0};
+        while ((buf = fgets(in, 50, stdin)) != NULL) {
+                while (*buf != '#') buf++;
+                k = 0;
+                for (int i = 1; i < 6; i++)
+                        k = 16*k + val(*(buf+i));
+                point_t d = go[*(buf+6) - '0'];
+                p[n] = (point_t){.i = p[n-1].i+d.i*k, .j = p[n-1].j+d.j*k};
+                n++;
+        }
+
+        qsort(p, --n, sizeof(point_t), &cmp_point);
+
+        for (int64_t i = 0, ia = 0; i < n-1; i++) {
+                a[ia++] = p[i].j;
+                if (p[i].i != p[i+1].i) {
+                        qsort(a, ia, sizeof(int64_t), &cmp_int64);
+                        ia = removedoubles(a, ia);
+                        t += linelen(a, ia) * (p[i+1].i - p[i].i + 1) -
+                            overlaplen(a, ia, olda, nolda);
+                        nolda = ia;
+                        memcpy(olda, a, nolda * sizeof(int64_t));
+                }
+        }
+
+        printf("%" PRId64 "\n", t);
+        return 0;
+}