pass another error case

go/alphametics/alphametics.go

@@ -13,9 +13,12 @@ func Solve(input string) (map[string]int, error) {
 	if err != nil {
 		return nil, err
 	}
-	if equation.nonUniqueValues() {
+	if equation.onlyTwoUniqueLetters() {
 		return nil, fmt.Errorf("solution must have unique value for each letter")
 	}
+	if equation.addendIsLongerThanSum() {
+		return nil, fmt.Errorf("leading zero solution is invalid")
+	}
 
 	letters := equation.uniqueLetters()
 	for {
@@ -80,10 +83,19 @@ func (e equation) isLeadingZero(letterToNumber map[string]int) bool {
 	return false
 }
 
-func (e equation) nonUniqueValues() bool {
+func (e equation) onlyTwoUniqueLetters() bool {
 	return len(e.uniqueLetters()) == 2
 }
 
+func (e equation) addendIsLongerThanSum() bool {
+	for _, addend := range e.addends {
+		if len(addend) > len(e.sum) {
+			return true
+		}
+	}
+	return false
+}
+
 func translate(letterToNumber map[string]int, word string) int {
 	numbers := ""
 	for _, letter := range word {

go/alphametics/cases_test.go

@@ -21,11 +21,11 @@ var testCases = []struct {
 		input:         "A == B",
 		errorExpected: true,
 	},
-	// {
-	// 	description:   "leading zero solution is invalid",
-	// 	input:         "ACA + DD == BD",
-	// 	errorExpected: true,
-	// },
+	{
+		description:   "leading zero solution is invalid",
+		input:         "ACA + DD == BD",
+		errorExpected: true,
+	},
 	{
 		description: "puzzle with two digits final carry",
 		input:       "A + A + A + A + A + A + A + A + A + A + A + B == BCC",