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nqueens-idiomatic.go
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nqueens-idiomatic.go
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/*
ported from nqueens.c
assuming FORCE_TIED_TASKS = FALSE
MANUAL_CUTOFF = FALSE
IF_CUTOFF = FALSE
*/
package main
import (
"flag"
"fmt"
"os"
"runtime"
"strconv"
"sync"
)
var solutions = [...]int{
1,
0,
0,
2,
10, /* 5 */
4,
40,
92,
352,
724, /* 10 */
2680,
14200,
73712,
365596,
}
var MAX_SOLUTIONS = cap(solutions) // cap() and len() are guaranteed to fit into an int
var total_count int
/*
* <a> contains array of <n> queen positions. Returns 1
* if none of the queens conflict, and returns 0 otherwise.
*/
// instead of passing a pointer, we use go's "slices", which are
// already pointers to array (regions). []int is a slice of the whole array.
func ok(n int, a []rune) bool {
// i, j declared implicitly in for loops
var p, q rune
for i := 0; i < n; i++ {
p = rune(a[i])
for j := i + 1; j < n; j++ {
q = rune(a[j])
if q == p || q == p-rune(j-i) || q == p+rune(j-i) {
return false
}
}
}
return true
}
func nqueens_ser(n int, j int, a []rune, solutions *int) {
var res int
if n == j {
*solutions = 1
return
}
*solutions = 0
/* try each possible position for queen <j> */
for i := 0; i < n; i++ {
/* allocate a temporary array and copy <a> into it */
a[j] = rune(i)
if ok(j+1, a) {
nqueens_ser(n, j+1, a, &res)
*solutions += res
}
}
}
func nqueens(n int, j int, a []rune, solutions *int, depth int) {
var csols []int
if n == j {
/* good solution, count it */
*solutions = 1
return
}
*solutions = 0
csols = make([]int, n) // allocates and zeroes (!)
//memset(csols, 0, ...)
var wg sync.WaitGroup
/* try each possible position for queen <j> */
for i := 0; i < n; i++ {
wg.Add(1)
//#pragma omp task untied
i := i //http://golang.org/doc/faq#closures_and_goroutines
go func(wg *sync.WaitGroup) {
defer (*wg).Done()
b := make([]rune, len(a))
copy(b, a)
b[j] = rune(i)
if ok(j+1, b) {
nqueens(n, j+1, b, &csols[i], depth)
}
}(&wg)
}
//#pragma omp taskwait
wg.Wait()
for i := 0; i < n; i++ {
*solutions += csols[i]
}
}
func find_queens(size int) {
total_count = 0
fmt.Printf("Computing N-Queens algorithm (n=%d)\n", size)
//#pragma omp parallel
{
//#pragma omp single
{
a := make([]rune, size)
nqueens(size, 0, a, &total_count, 0)
}
}
fmt.Println(" completed!")
}
func verify_queens(size int) int {
if size > MAX_SOLUTIONS {
fmt.Println("size is ", size, "while MAX_SOLUTIONS is ", MAX_SOLUTIONS)
return -1
}
if total_count == solutions[size-1] {
fmt.Println("OK: total_count is", total_count, " solutions[size-1] is ", solutions[size-1])
return 0
}
fmt.Println("Verification failed! Total count is", total_count, ", expected: ", solutions[size-1])
return -2
}
func main() {
bindThreads := os.Getenv("OMP_PROC_BIND")
if bindThreads == "TRUE" {
runtime.LockOSThread()
}
numThreads, err := strconv.Atoi(os.Getenv("OMP_NUM_THREADS"))
if err != nil || numThreads < 1 {
numThreads = runtime.NumCPU()
}
runtime.GOMAXPROCS(numThreads)
boardSize := flag.Int("n", 8, "Board size")
flag.Parse()
start := Wtime_sec()
find_queens(*boardSize)
end := Wtime_sec()
fmt.Printf("Program time: %.6f s\n", end-start)
verify_queens(*boardSize)
}