From a3319c804b0ef3a6d9e91909e5b510feeb8baab9 Mon Sep 17 00:00:00 2001 From: Sebastiano Tronto Date: Sun, 24 Dec 2023 20:12:34 +0100 Subject: Added solution for 24 --- 2023/24/24a.c | 76 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 76 insertions(+) create mode 100644 2023/24/24a.c (limited to '2023/24/24a.c') diff --git a/2023/24/24a.c b/2023/24/24a.c new file mode 100644 index 0000000..6c75c08 --- /dev/null +++ b/2023/24/24a.c @@ -0,0 +1,76 @@ +#include +#include +#include + +#define N 300 +#define XMIN 2e14 +#define XMAX 4e14 +#define eps 1e-6 + +#define ABS(x) ((x)>0?(x):-(x)) + +typedef struct { double x, y, z; } point_t; +typedef struct { point_t p, v; } line_t; + +char *buf, line[N]; +int n, s; +line_t l[N]; + +bool isnum(char c) { return (c >= '0' && c <= '9') || c == '-'; } + +line_t readl(char *buf) { + double a[6]; + for (int i = 0; i < 6; i++) { + a[i] = (double)atoll(buf); + while (isnum(*buf)) buf++; + while (*buf != '\n' && !isnum(*buf)) buf++; + } + return (line_t) { + .p = (point_t){.x = a[0], .y = a[1], .z = a[2]}, + .v = (point_t){.x = a[3], .y = a[4], .z = a[5]} + }; +} + +double det(double a, double b, double c, double d) { return a*d-b*c; } + +bool parallel2d(line_t l1, line_t l2) { + double d = det(l1.v.x, l2.v.x, l1.v.y, l2.v.y); + return ABS(d) < eps; +} + +point_t collide2d(line_t l1, line_t l2, double *t1, double *t2) { + double a1 = l1.v.x; + double b1 = -l2.v.x; + double c1 = l2.p.x - l1.p.x; + double a2 = l1.v.y; + double b2 = -l2.v.y; + double c2 = l2.p.y - l1.p.y; + + double d = det(a1, b1, a2, b2); + *t1 = det(c1, b1, c2, b2) / d; + *t2 = det(a1, c1, a2, c2) / d; + + double x = l1.p.x + l1.v.x * (*t1); + double y = l1.p.y + l1.v.y * (*t1); + + return (point_t) {.x = x, .y = y}; +} + +int main() { + for (n = 0; (buf = fgets(line, N, stdin)) != NULL; n++) + l[n] = readl(buf); + + for (int i = 0; i < n; i++) { + for (int j = i+1; j < n; j++) { + if (parallel2d(l[i], l[j])) continue; + double t1, t2; + point_t p = collide2d(l[i], l[j], &t1, &t2); + if (t1 < -eps || t2 < -eps) continue; + s += p.x > XMIN-eps && p.x < XMAX+eps && + p.y > XMIN-eps && p.y < XMAX+eps; + } + } + + printf("%d\n", s); + return 0; +} -- cgit v1.3