Brute-force solution of the Zebra Puzzle https://code.energy/solving-zebra-puzzle/

zebra-puzzle.go

// Brute-force solution of the Zebra Puzzle
// https://code.energy/solving-zebra-puzzle/
//
// Result:
// Norwegian from 1 house drinks water.
// Japanese from 5 house owns zebra.

package main

import (
  "fmt"
)

func contains(values []int, value int) bool {
  for _, n := range values {
    if n == value {
      return true
    }
  }
  return false
}

func addIndexRecursive(indexes []int, ch chan []int, n int) {
  if len(indexes) == 5 {
    ch <- indexes
    return
  }
  for i := 0; i < n ; i++ {
    if contains(indexes, i) {
      continue
    }
    indexes = append(indexes, i)
    addIndexRecursive(indexes, ch, n)
    indexes = indexes[:len(indexes)-1]
  }
}

func allCombinations(n int) chan []int {
  ch := make(chan []int)
  go func(ch chan []int) {
    indexes := []int {}
    addIndexRecursive(indexes, ch, n)
    close(ch)
  }(ch)
  return ch
}


func match(indexes1 []int, value1 int, indexes2[]int, value2 int) bool {
  if (indexes1[0] != value1 || indexes2[0] != value2) &&
    (indexes1[1] != value1 || indexes2[1] != value2) &&
    (indexes1[2] != value1 || indexes2[2] != value2) &&
    (indexes1[3] != value1 || indexes2[3] != value2) &&
    (indexes1[4] != value1 || indexes2[4] != value2) {
    return false
  }
  return true
}

func rightOf(indexes1 []int, value1 int, indexes2[]int, value2 int) bool {
  if (indexes1[1] != value1 || indexes2[0] != value2) &&
    (indexes1[2] != value1 || indexes2[1] != value2) &&
    (indexes1[3] != value1 || indexes2[2] != value2) &&
    (indexes1[4] != value1 || indexes2[3] != value2) {
    return false
  }
  return true
}

func nextTo(indexes1 []int, value1 int, indexes2[]int, value2 int) bool {
  if (indexes1[0] != value1 || indexes2[1] != value2) &&
    (indexes1[1] != value1 || indexes2[0] != value2 && indexes2[2] != value2) &&
    (indexes1[2] != value1 || indexes2[1] != value2 && indexes2[3] != value2) &&
    (indexes1[3] != value1 || indexes2[2] != value2 && indexes2[4] != value2) &&
    (indexes1[4] != value1 || indexes2[3] != value2) {
    return false
  }
  return true
}

const (
  englishman = iota
  ukrainian
  norwegian
  japanese
  spaniard
)

const (
  red = iota
  green
  ivory
  blue
  yellow
)

const (
  milk = iota
  orange
  water
  tea
  coffee
)

const (
  oldGold = iota
  kools
  chesterfields
  luckyStrike
  parliaments
)

const (
  dog = iota
  snails
  horse
  zebra
  fox
)

func main() {
  nationsTitles := [5]string {"Englishman", "Ukrainian", "Norwegian", "Japanese", "Spaniard"}

  for iNations := range allCombinations(5) {
    if !(iNations[0] == norwegian) {
      continue
    }
    for iSmokes := range allCombinations(5) {
      if !match(iNations, japanese, iSmokes, parliaments) {
        continue
      }
      for iColors := range allCombinations(5) {
        if !match(iNations, englishman, iColors, red) ||
          !match(iSmokes, kools, iColors, yellow) ||
          !rightOf(iColors, green, iColors, ivory) ||
          !nextTo(iNations, norwegian, iColors, blue) {
          continue
        }
        for iDrinks := range allCombinations(5) {
          if !(iDrinks[2] == 0) ||
            !match(iDrinks, coffee, iColors, green) ||
            !match(iNations, ukrainian, iDrinks, tea) ||
            !match(iSmokes, luckyStrike, iDrinks, orange) {
            continue
          }
          for iPets := range allCombinations(5) {
            if !match(iNations, spaniard, iPets, dog) ||
              !match(iSmokes, oldGold, iPets, snails) ||
              !nextTo(iSmokes, chesterfields, iPets, fox) ||
              !nextTo(iSmokes, kools, iPets, horse) {
              continue
            }

            for i, iDrink := range iDrinks {
              if iDrink == water {
                fmt.Println(nationsTitles[iNations[i]], "from", i + 1, "house drinks water.")
              }
            }
            for i, iPet := range iPets {
              if iPet == zebra {
                fmt.Println(nationsTitles[iNations[i]], "from", i + 1, "house owns zebra.")
              }
            }
          }
        }
      }
    }
  }
}