//main entry function that calls the right
//functions for getting sodoku answer
func (inst *Solutionizer) GetSodokuSolution(board *sodoku.Board) string {
inst.possibilities = 0
pass := inst.SetIndicesWithLeastPossibleChoices(board)
if !pass {
panic("Can't be solved!")
return ""
}
return board.GetStringFormat()
}
//for a particular empty index, returns the
//numbers available that can poltentially be
//inserted in that index
func (inst *Solutionizer) getPossibilities(i, j int, board *sodoku.Board) []int {
families := board.GetFamilies(i, j)
availableNumbers := 987654321
for _, family := range families {
availableNumbers = inst.availableNumbers(availableNumbers, family)
}
numsAvailable := inst.getPossibilitiesFromAvailableNumbers(availableNumbers)
return numsAvailable
}
//retrieves the family with the least
//free options to choose from. For example
//if a particular row only has one blank
//indices then we know we can fill that entry
//with 100% certainty(the unused number will go there)
//returns true if solution was found
func (inst *Solutionizer) SetIndicesWithLeastPossibleChoices(board *sodoku.Board) bool {
toBeFilled := board.GetEmptyIndices()
if len(toBeFilled) <= 0 && board.IsBoardComplete() {
return true
}
oppertunityFound := false
oppertunities := [9][]oppertunity{}
boardChange := false
for _, v := range toBeFilled {
i, j := v[0], v[1]
numAvailable := inst.getPossibilities(i, j, board)
length := len(numAvailable)
//if no oppertunities or certainties were found then
//we are dealing with a faulty/broken board
if length <= 0 {
return false
//if we only have one choice to choose from then we know 100% we can set it
} else if length == 1 {
//set indices for relatives
board.SetEntry(i, j, numAvailable[0])
boardChange = true
//other wise we track available oppurtunities thats ordered
//based on amount of numbers available
} else {
oppertunityFound = true
oppertunities[length] = append(oppertunities[length], oppertunity{i, j, numAvailable})
}
}
//if board was changed we call recursion on updated board
if boardChange {
return inst.SetIndicesWithLeastPossibleChoices(board)
//else if at least one oppurtunity was found
//we insert oppurtunity and recompute recursion
//notice how oppertunities are traverse based on order
//of minimum possibilities. This gives it a much higher chance
//of success
} else if oppertunityFound {
//make copy of current entries before any alterations
originalEntry := inst.copy(board.Entries)
inst.possibilities += 1
for _, ops := range oppertunities {
for _, op := range ops {
if len(op.Entries) <= 0 {
continue
}
for _, v := range op.Entries {
board.SetEntry(op.I, op.J, v)
pass := inst.SetIndicesWithLeastPossibleChoices(board)
//if recursion returns true
if pass {
return true
//otherwise if this oppertunity wasnt the best choice
//we set it back to 0 and try next oppertunity
} else {
board.SetEntries(originalEntry)
}
}
}
}
}
return false
}
