Merge 0c95f86 into d8d2dea

README.md

@@ -416,4 +416,5 @@ problems from
 * [Day 417](https://github.com/vaskoz/dailycodingproblem-go/issues/842)
 * [Day 418](https://github.com/vaskoz/dailycodingproblem-go/issues/844)
 * [Day 419](https://github.com/vaskoz/dailycodingproblem-go/issues/846)
+* [Day 420](https://github.com/vaskoz/dailycodingproblem-go/issues/848)
 

day420/problem.go

@@ -0,0 +1,28 @@
+package day420
+
+// PerfectNth returns the n-th perfect number.
+// A perfect number is one where the digits sum to 10.
+// A panic will happen if the argument is less than 1.
+func PerfectNth(n int) int {
+	if n < 1 {
+		panic("n must be greater than 0")
+	}
+
+	perfectNum := 10 // 10 is the seed value.
+	for n != 0 {
+		perfectNum += 9
+		digits := perfectNum
+		sum := 0
+
+		for digits != 0 {
+			sum += (digits % 10)
+			digits /= 10
+		}
+
+		if sum == 10 {
+			n--
+		}
+	}
+
+	return perfectNum
+}

day420/problem_test.go

@@ -0,0 +1,41 @@
+package day420
+
+import "testing"
+
+// nolint
+var testcases = []struct {
+	n, expected int
+}{
+	{1, 19},
+	{2, 28},
+	{10, 109},
+}
+
+func TestPerfectNth(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range testcases {
+		if result := PerfectNth(tc.n); result != tc.expected {
+			t.Errorf("Expected %v got %v", tc.expected, result)
+		}
+	}
+}
+
+func TestPerfectNthPanic(t *testing.T) {
+	t.Parallel()
+
+	defer func() {
+		if err := recover(); err == nil {
+			t.Errorf("Expected a panic for an argument less than 1")
+		}
+	}()
+	PerfectNth(0)
+}
+
+func BenchmarkPerfectNth(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			PerfectNth(tc.n)
+		}
+	}
+}