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6x6 Hotel Key Card Counter
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/* 6x6 Hotel Key Card Counter | |
* $ cc -fopenmp -O3 -march=native keycount.c | |
* Ref: https://possiblywrong.wordpress.com/2020/10/24/counting-hotel-key-cards/ | |
*/ | |
#include <stdio.h> | |
static long long | |
transpose(long long x) | |
{ | |
return (x << 5 & 0x408102040) | | |
(x << 10 & 0x204081000) | | |
(x << 15 & 0x102040000) | | |
(x << 20 & 0x081000000) | | |
(x << 25 & 0x040000000) | | |
(x >> 0 & 0x810204081) | | |
(x >> 5 & 0x020408102) | | |
(x >> 10 & 0x000810204) | | |
(x >> 15 & 0x000020408) | | |
(x >> 20 & 0x000000810) | | |
(x >> 25 & 0x000000020); | |
} | |
static long long | |
flipv(long long x) | |
{ | |
return (x >> 30 & 0x00000003f) | | |
(x >> 18 & 0x000000fc0) | | |
(x >> 6 & 0x00003f000) | | |
(x << 6 & 0x000fc0000) | | |
(x << 18 & 0x03f000000) | | |
(x << 30 & 0xfc0000000); | |
} | |
static int | |
valid(long long x) | |
{ | |
int v = 0; | |
long long t; | |
t = transpose(x); v += t == x; | |
t = flipv(t); v += t == x; | |
t = transpose(t); v += t == x; | |
t = flipv(t); v += t == x; | |
t = transpose(t); v += t == x; | |
t = flipv(t); v += t == x; | |
t = transpose(t); v += t == x; | |
return !v; | |
} | |
int | |
main(void) | |
{ | |
long long total = 0; | |
#pragma omp parallel for | |
for (int n = 0; n < 1<<8; n++) { | |
long long subtotal = 0; | |
for (long long i = 0; i < 1LL<<28; i++) { | |
subtotal += valid(i<<8 | n); | |
} | |
#pragma omp atomic | |
total += subtotal; | |
} | |
printf("%lld\n", total/8); | |
} |
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