recursive solver

recsolver.go

func (v verbalSum) recursiveSolve(
	letters []rune, digits []int, mapping map[rune]int,
) (combinations int, solutions int) {
	if len(letters) == 0 {
		if v.isValidSolution(mapping) {
			fmt.Printf("Found   %v\n", v.solutionString(mapping))
			return 1, 1 // one solution tried, one solution found
		}
		return 1, 0 // one solution tried, zero solution found
	}
	letter := letters[0] // take the first letter
	combinations, solutions = 0, 0
	for i, digit := range digits { // try all digits for the letter "letter"
		mapping[letter] = digit
		c, s := v.recursiveSolve(letters[1:], withoutItem(digits, i), mapping)
		combinations += c
		solutions += s
	}
	delete(mapping, letter)
	return
}