euler / go / src / euler / 24.go

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65``` ```/* A permutation is an ordered arrangement of objects. For example, 3124 is one possible permutation of the digits 1, 2, 3 and 4. If all of the permutations are listed numerically or alphabetically, we call it lexicographic order. The lexicographic permutations of 0, 1 and 2 are: 012 021 102 120 201 210 What is the millionth lexicographic permutation of the digits 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9? */ package main import ( "fmt" "sort" ) type Reversed []int func (r Reversed) Len() int { return len(r) } func (r Reversed) Less(i, j int) bool { return r[i] > r[j] } func (r Reversed) Swap(i, j int) { r[i], r[j] = r[j], r[i] } func isLast(items []int) bool { return sort.IsSorted(Reversed(items)) } func lexicalPermutations(items []int) chan []int { out := make(chan []int) sort.Ints(items) go func() { for { out <- items if isLast(items) { close(out) return } } }() return out } var items = []int{0, 1, 2} func e24() { var i = []int{3, 1, 2} fmt.Printf("%v\n", isLast(i)) sort.Sort(Reversed(i)) fmt.Printf("%v\n", i) fmt.Printf("%v\n", isLast(i)) } func init() { register("24", e24) } ```