From 1f75d7c9ebec207c8193754792076dc66eba9713 Mon Sep 17 00:00:00 2001
From: Sebastiano Tronto <sebastiano@tronto.net>
Date: Tue, 19 Dec 2023 15:54:12 +0100
Subject: Added solutions for 15, 16, 17, 18 and 19

---
 2023/18/18b.c | 92 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 92 insertions(+)
 create mode 100644 2023/18/18b.c

(limited to '2023/18')

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;
+}
-- 
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