Merge b241e3c into fe69e29

README.md

@@ -328,6 +328,7 @@ problems from
 * [Day 315](https://github.com/vaskoz/dailycodingproblem-go/issues/642)
 * [Day 316](https://github.com/vaskoz/dailycodingproblem-go/issues/644)
 * [Day 317](https://github.com/vaskoz/dailycodingproblem-go/issues/645)
+* [Day 318](https://github.com/vaskoz/dailycodingproblem-go/issues/648)
 * [Day 319](https://github.com/vaskoz/dailycodingproblem-go/issues/649)
 * [Day 320](https://github.com/vaskoz/dailycodingproblem-go/issues/650)
 * [Day 321](https://github.com/vaskoz/dailycodingproblem-go/issues/651)

day318/problem.go

@@ -0,0 +1,53 @@
+package day318
+
+// NumberOfValidPlayListsRec is a recursive solution.
+func NumberOfValidPlayListsRec(required, downloaded, buffer int) int {
+	if buffer >= downloaded {
+		return 0
+	}
+
+	if required == 0 {
+		return 1
+	}
+
+	downloadParam := downloaded
+
+	if buffer != 0 {
+		downloadParam--
+	}
+
+	return downloaded * NumberOfValidPlayListsRec(required-1, downloadParam, max(0, buffer-1))
+}
+
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+
+	return b
+}
+
+// NumberOfValidPlayListsIterative is an iterative solution.
+func NumberOfValidPlayListsIterative(required, downloaded, buffer int) int {
+	if buffer >= downloaded {
+		return 0
+	}
+
+	total := 1
+	available := downloaded
+
+	for i := 0; i <= buffer; i++ {
+		total *= available
+		available--
+	}
+
+	if available < downloaded {
+		available++
+	}
+
+	for i := buffer + 1; i < required; i++ {
+		total *= available
+	}
+
+	return total
+}

day318/problem_test.go

@@ -0,0 +1,54 @@
+package day318
+
+import "testing"
+
+// nolint
+var testcases = []struct {
+	N, M, B  int
+	expected int
+}{
+	{4, 2, 1, 2},
+	{4, 2, 0, 16},
+	{4, 2, 2, 0},
+	{9, 2, 1, 2},
+	{9, 2, 0, 512},
+	{9, 3, 2, 6},
+	{9, 3, 1, 768},
+	{9, 3, 0, 19683},
+}
+
+func TestNumberOfValidPlayListsRec(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range testcases {
+		if result := NumberOfValidPlayListsRec(tc.N, tc.M, tc.B); result != tc.expected {
+			t.Errorf("Expected %v, got %v", tc.expected, result)
+		}
+	}
+}
+
+func BenchmarkNumberOfValidPlayListsRec(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			NumberOfValidPlayListsRec(tc.N, tc.M, tc.B)
+		}
+	}
+}
+
+func TestNumberOfValidPlayListsIterative(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range testcases {
+		if result := NumberOfValidPlayListsIterative(tc.N, tc.M, tc.B); result != tc.expected {
+			t.Errorf("Expected %v, got %v", tc.expected, result)
+		}
+	}
+}
+
+func BenchmarkNumberOfValidPlayListsIterative(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			NumberOfValidPlayListsIterative(tc.N, tc.M, tc.B)
+		}
+	}
+}