Created
December 9, 2012 05:58
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Project Euler #24 in Go - Answer: [2 7 8 3 9 1 5 4 6 0]
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| package main | |
| import ( | |
| "fmt" | |
| ) | |
| var _ = fmt.Printf | |
| const Max = 10 | |
| const Index = 1000000 - 1 | |
| func main() { | |
| numbers := make([]byte, 0, Max) | |
| for i := 0; i < Max; i++ { | |
| numbers = append(numbers, byte(i)) | |
| } | |
| count := 1 | |
| for i := 2; i <= Max; i++ { | |
| count *= i | |
| } | |
| if count > Index { | |
| count = Index+1 | |
| } | |
| perms = make([][Max]byte, 0, count) | |
| perm(numbers, 0, len(numbers)) | |
| if len(perms) > Index { | |
| fmt.Println(perms[Index]) | |
| } else { | |
| fmt.Println("only", len(perms), "perms generated") | |
| } | |
| } | |
| var perms [][Max]byte | |
| func perm(numbers []byte, lo, hi int) { | |
| if len(perms) > Index { | |
| return | |
| } | |
| if hi-lo < 2 { | |
| var p [Max]byte | |
| copy(p[:], numbers) | |
| perms = append(perms, p) | |
| return | |
| } | |
| for i := 1; i < hi-lo+1; i++ { | |
| rotateR(numbers, lo, lo+i) | |
| perm(numbers, lo+1, hi) | |
| rotateL(numbers, lo, lo+i) | |
| } | |
| } | |
| func rotateL(numbers []byte, lo, hi int) { | |
| for i := lo + 1; i < hi; i++ { | |
| numbers[i-1], numbers[i] = numbers[i], numbers[i-1] | |
| } | |
| } | |
| func rotateR(numbers []byte, lo, hi int) { | |
| for i := hi - 1; i > lo; i-- { | |
| numbers[i-1], numbers[i] = numbers[i], numbers[i-1] | |
| } | |
| } |
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