Created
March 10, 2012 20:08
-
-
Save AsadR/2012876 to your computer and use it in GitHub Desktop.
Dumb Eight Queen Solution in C
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
/* | |
* 8-Queen problem solution in C | |
* written by Asad ur Rehman <asad.rehman@gmail.com> | |
* | |
* gcc -O3 -fomit-frame-pointer -fstrict-aliasing -momit-leaf-frame-pointer -fno-tree-pre -falign-loops -funroll-loops queen.c -o queen | |
* | |
* real 0m0.445s | |
* user 0m0.279s | |
* sys 0m0.165s | |
* | |
* Mon Feb 20 17:44:45 PKT 2012 | |
* | |
*/ | |
#include <stdio.h> | |
#include <string.h> | |
#include <stdlib.h> | |
#include <stdint.h> | |
#define X_FROM_I(i) (i / 8) | |
#define Y_FROM_I(i) (i % 8) | |
#define I_FROM_XY(x,y) ((y*8)+x) | |
static unsigned char *cache; | |
static long long cache_hit; | |
static long long cache_miss; | |
// mark horizontal, vertical and both diagonal kill zones for the queen | |
// (also mark the queen's location) | |
void mark_killzone(char *board, int index) | |
{ | |
int i; | |
int x, y; | |
x = X_FROM_I(index); | |
y = Y_FROM_I(index); | |
// '.' means the place is empty | |
// 'X' means there's a queen there | |
// 'O' means it's in some queen's kill zone | |
for(i = 0; i < 64; i++) | |
if( X_FROM_I(i) == x && Y_FROM_I(i) == y ) | |
board[i] = 'X'; | |
else if( X_FROM_I(i) == x || Y_FROM_I(i) == y || (x-y) == (X_FROM_I(i)-Y_FROM_I(i)) || (x+y) == (X_FROM_I(i)+Y_FROM_I(i)) ) | |
board[i] = 'O'; | |
} | |
// returns a unique 32 bit hash for each board configuration | |
// groups of 4 bits, each group specifying position of the queen | |
// at that row 0=not present, 1=0'th index, 2=1st index, etc. | |
uint32_t board_hash(char *board) | |
{ | |
int i, j; | |
uint32_t hash = 0; | |
for( i = 0; i < 8; i++ ) | |
{ | |
unsigned char f = 0x0; | |
for( j = 0; j < 8; j++ ) | |
{ | |
if(board[I_FROM_XY(i,j)] == 'X') | |
{ | |
f = j+1; | |
break; | |
} | |
} | |
hash <<= 4; | |
hash |= (f & 0xF); | |
} | |
/* for(i = 0; i < 64; i++) | |
printf("%c%c", board[i], ((i+1)%8)?' ':'\n'); | |
printf("hash: %X\n", hash); */ | |
return hash; | |
} | |
int check_cache(char *board) | |
{ | |
uint32_t hash = board_hash(board); // use this as a bit index | |
uint32_t cache_byte_offset = hash / 8; | |
uint32_t bit_offset = hash % 8; | |
unsigned char b = cache[cache_byte_offset]; | |
if(b & (0x1 << bit_offset)) { | |
cache_hit++; | |
return 1; | |
} | |
b |= (0x1 << bit_offset); | |
cache[cache_byte_offset] = b; | |
cache_miss++; | |
return 0; | |
} | |
void try_inserting_queens(char *board) | |
{ | |
if(check_cache(board)) | |
return; | |
int i; | |
int q = 0; | |
for(i = 0; i < 64; i++) | |
{ | |
char c = board[i]; | |
switch(c) | |
{ | |
char *board_copy; | |
case '.': // is empty location | |
board_copy = malloc(64); | |
memcpy(board_copy, board, 64); | |
mark_killzone(board_copy, i); | |
try_inserting_queens(board_copy); | |
free(board_copy); | |
break; | |
case 'X': // there's a queen already here | |
q++; | |
break; | |
case 'O': // some queen's killzone is here | |
break; | |
default: | |
break; | |
} | |
if(q == 8) | |
{ | |
printf("8 queens solution found:\n"); | |
for(i = 0; i < 64; i++) | |
printf("%c%c", board[i], ((i+1)%8)?' ':'\n'); | |
printf("\n"); | |
break; // no need to process this further | |
} | |
} | |
} | |
int main() | |
{ | |
char board[64]; | |
memset(board, '.', 64); | |
cache_hit = 0; | |
cache_miss = 0; | |
cache = malloc(536870912); // 2 ^ 32 bits, for 2^32 possible board configurations (4 bits per row) | |
if(cache == NULL) | |
{ | |
perror("unable to allocate memory"); | |
exit(-1); | |
} | |
memset(cache, 0x0, 536870912); | |
try_inserting_queens(board); | |
printf("cache hit: %qu\ncache miss: %qu\n", cache_hit, cache_miss); | |
free(cache); | |
return 0; | |
} |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment