48 lines
824 B
Go
48 lines
824 B
Go
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package ints
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// Faculty returns the faculty of i.
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func Faculty(i int) int {
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if i < 2 {
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return 1
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}
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return i * Faculty(i-1)
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}
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// Faculty64 returns the faculty of i.
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func Faculty64(i int64) int64 {
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if i < 2 {
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return 1
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}
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return i * Faculty64(i-1)
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}
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// Permutations returns all possible permutations of the the set integers.
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func Permutations(set []int) [][]int {
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var n = len(set)
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if n == 0 {
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return nil
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}
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var res = make([][]int, 0, Faculty(n))
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var p = append([]int(nil), set...)
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var c = make([]int, n)
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res = append(res, append([]int(nil), p...))
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i := 0
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for i < n {
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if c[i] < i {
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if i%2 == 0 {
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p[0], p[i] = p[i], p[0]
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} else {
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p[c[i]], p[i] = p[i], p[c[i]]
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}
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res = append(res, append([]int(nil), p...))
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c[i] = c[i] + 1
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i = 0
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} else {
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c[i] = 0
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i++
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}
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}
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return res
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}
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