// Port of some Python's itertools
// ================================
// A.K.A. my first piece of Go code
//
// Written by Nuno Antunes, 2012-08-08
// GitHub: https://github.com/ntns
//
// Python docs: http://docs.python.org/library/itertools.html
// Python source: http://svn.python.org/view/python/tags/r271/Modules/itertoolsmodule.c?view=markup

package main

import "fmt"

func combinations(iterable []int, r int) {
    pool := iterable
    n := len(pool)

    if r > n {
        return
    }

    indices := make([]int, r)
    for i := range indices {
        indices[i] = i
    }

    result := make([]int, r)
    for i, el := range indices {
        result[i] = pool[el]
    }

    fmt.Println(result)

    for {
        i := r - 1
        for ; i >= 0 && indices[i] == i+n-r; i -= 1 {
        }

        if i < 0 {
            return
        }

        indices[i] += 1
        for j := i + 1; j < r; j += 1 {
            indices[j] = indices[j-1] + 1
        }

        for ; i < len(indices); i += 1 {
            result[i] = pool[indices[i]]
        }
        fmt.Println(result)

    }

}

func permutations(iterable []int, r int) {
    pool := iterable
    n := len(pool)

    if r > n {
        return
    }

    indices := make([]int, n)
    for i := range indices {
        indices[i] = i
    }

    cycles := make([]int, r)
    for i := range cycles {
        cycles[i] = n - i
    }

    result := make([]int, r)
    for i, el := range indices[:r] {
        result[i] = pool[el]
    }

    fmt.Println(result)

    for n > 0 {
        i := r - 1
        for ; i >= 0; i -= 1 {
            cycles[i] -= 1
            if cycles[i] == 0 {
                index := indices[i]
                for j := i; j < n-1; j += 1 {
                    indices[j] = indices[j+1]
                }
                indices[n-1] = index
                cycles[i] = n - i
            } else {
                j := cycles[i]
                indices[i], indices[n-j] = indices[n-j], indices[i]

                for k := i; k < r; k += 1 {
                    result[k] = pool[indices[k]]
                }

                fmt.Println(result)

                break
            }
        }

        if i < 0 {
            return
        }

    }

}

func product(argsA, argsB []int) {

    pools := [][]int{argsA, argsB}
    npools := len(pools)
    indices := make([]int, npools)

    result := make([]int, npools)
    for i := range result {
        result[i] = pools[i][0]
    }

    fmt.Println(result)

    for {
        i := npools - 1
        for ; i >= 0; i -= 1 {
            pool := pools[i]
            indices[i] += 1

            if indices[i] == len(pool) {
                indices[i] = 0
                result[i] = pool[0]
            } else {
                result[i] = pool[indices[i]]
                break
            }

        }

        if i < 0 {
            return
        }

        fmt.Println(result)
    }
}

func main() {
    fmt.Println("Itertools combinations in Go:")
    // combinations('ABCD', 2) --> AB AC AD BC BD CD
    // combinations(range(4), 3) --> 012 013 023 123
    fmt.Printf("iterable = %s, r = %d", "[]int{1, 2, 3, 4, 5, 6}", 3)
    fmt.Println()
    combinations([]int{1, 2, 3, 4, 5, 6}, 3)

    fmt.Println("Itertools permutations in Go:")
    // permutations('ABCD', 2) --> AB AC AD BA BC BD CA CB CD DA DB DC
    // permutations(range(3)) --> 012 021 102 120 201 210
    fmt.Printf("iterable = %s, r = %d", "[]int{1, 2, 3, 4}", 3)
    fmt.Println()
    permutations([]int{1, 2, 3, 4}, 3)

    fmt.Println("Itertools product in Go:")
    // product('ABCD', 'xy') --> Ax Ay Bx By Cx Cy Dx Dy
    // product(range(2), repeat=3) --> 000 001 010 011 100 101 110 111
    fmt.Printf("iterables = %s, %s", "[]int{1, 2, 3}", "[]int{10, 20, 30}")
    fmt.Println()
    product([]int{1, 2, 3}, []int{10, 20, 30})

}

package main

import (
    "fmt"
    "github.com/kokardy/listing"
)

func main() {

    ss := listing.StringReplacer([]string{
        "A", "B", "C", "D",
    })
    //You can use any types that implement listing.Replacer interface (Len(), Replace([]int))


    select_num := 3
    repeatable := false
    buf := 5

    fmt.Println("Permutations")
    for perm := range listing.Permutations(ss, select_num, repeatable, buf) {
        fmt.Println(perm)
    }

    fmt.Println("Combinations")
    for comb := range listing.Combinations(ss, select_num, repeatable, buf) {
        fmt.Println(comb)
    }

}

package main
 
import (
    "fmt"
)
 
func main() {
    comb(5, 3, func(c []int) {
        fmt.Println(c)
    })
}
 
func comb(n, m int, emit func([]int)) {
    s := make([]int, m)
    last := m - 1
    var rc func(int, int)
    rc = func(i, next int) {
        for j := next; j < n; j++ {
            s[i] = j
            if i == last {
                emit(s)
            } else {
                rc(i+1, j+1)
            }
        }
        return
    }
    rc(0, 0)
}