/
combinatorics.go
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/
combinatorics.go
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/*
Copyright 2017, 2020 Andrew Medworth
This file is part of Gopoker, a set of miscellaneous poker-related functions
written in the Go programming language (http://golang.org).
Gopoker is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
Gopoker is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Affero General Public License for more details.
You should have received a copy of the GNU Affero General Public License
along with Gopoker. If not, see <http://www.gnu.org/licenses/>.
*/
package poker
// Reimplement some simple mathematical functions here to avoid float64 or big.Int conversions
func min(x, y int) int {
if x < y {
return x
} else {
return y
}
}
func max(x, y int) int {
if x > y {
return x
} else {
return y
}
}
func binomial(n, r int) int {
result := 1
for i := n; i > max(r, n-r); i-- {
result *= i
}
for i := min(r, n-r); i > 1; i-- {
result /= i
}
return result
}
// Compute all unique subsets of a set of cards, of a given size.
func AllCardCombinations(pack []Card, numRequired int) [][]Card {
result := make([][]Card, 0, binomial(len(pack), numRequired))
indices := make([]int, numRequired)
// Standard algorithm to enumerate k-combinations
// Start with the first numRequired elements of the array
for i := 0; i < numRequired; i++ {
indices[i] = i
}
for {
// Construct a combination
combination := make([]Card, numRequired)
for i := 0; i < numRequired; i++ {
combination[i] = pack[indices[i]]
}
result = append(result, combination)
// Advance to the next combination.
// First, find the first index, starting from the right,
// that's not part of a block pointing to the end of the array.
i := numRequired - 1
for i >= 0 && indices[i] == i+len(pack)-numRequired {
i--
}
if i < 0 {
// There is no such index: all indexes are at the end of the array.
// We've finished.
break
}
// Advance that index.
indices[i]++
// Reset all indexes to the right to be the immediate successors of
// the index we just advanced.
for j := i + 1; j < numRequired; j++ {
indices[j] = indices[j-1] + 1
}
}
return result
}