Day283

README.md

@@ -289,3 +289,4 @@ problems from
 * [Day 280](https://github.com/vaskoz/dailycodingproblem-go/issues/568)
 * [Day 281](https://github.com/vaskoz/dailycodingproblem-go/issues/572)
 * [Day 282](https://github.com/vaskoz/dailycodingproblem-go/issues/575)
+* [Day 283](https://github.com/vaskoz/dailycodingproblem-go/issues/577)

day283/problem.go

@@ -0,0 +1,68 @@
+package day283
+
+// RegularNumbersFaster returns n regular numbers
+// using brute force.
+func RegularNumbersFaster(n int) []int {
+	if n < 0 {
+		panic("negative values are not possible")
+	} else if n == 0 {
+		return []int{}
+	}
+	result := make([]int, n)
+	result[0] = 1
+	var i2, i3, i5 int
+	next2, next3, next5 := 2, 3, 5
+	for i := 1; i < n; i++ {
+		result[i] = min(next2, next3, next5)
+		if result[i] == next2 {
+			i2++
+			next2 = result[i2] * 2
+		}
+		if result[i] == next3 {
+			i3++
+			next3 = result[i3] * 3
+		}
+		if result[i] == next5 {
+			i5++
+			next5 = result[i5] * 5
+		}
+	}
+	return result
+}
+
+func min(vals ...int) int {
+	smallest := vals[0]
+	for _, v := range vals {
+		if v < smallest {
+			smallest = v
+		}
+	}
+	return smallest
+}
+
+// RegularNumbersBrute returns n regular numbers
+// using brute force.
+func RegularNumbersBrute(n int) []int {
+	if n < 0 {
+		panic("negative values are not possible")
+	}
+	result := make([]int, 0, n)
+	count := 0
+	for x := 1; count < n; x++ {
+		remain := repeatDivide(x, 2)
+		remain = repeatDivide(remain, 3)
+		remain = repeatDivide(remain, 5)
+		if remain == 1 {
+			result = append(result, x)
+			count++
+		}
+	}
+	return result
+}
+
+func repeatDivide(val, factor int) int {
+	for val%factor == 0 {
+		val /= factor
+	}
+	return val
+}

day283/problem_test.go

@@ -0,0 +1,70 @@
+package day283
+
+import (
+	"reflect"
+	"testing"
+)
+
+// nolint
+var testcases = []struct {
+	n        int
+	expected []int
+}{
+	{0, []int{}},
+	{1, []int{1}},
+	{2, []int{1, 2}},
+	{11, []int{1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15}},
+	{26, []int{1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 16, 18, 20, 24, 25, 27, 30, 32, 36, 40, 45, 48, 50, 54, 60}},
+}
+
+func TestRegularNumbersFaster(t *testing.T) {
+	t.Parallel()
+	for _, tc := range testcases {
+		if result := RegularNumbersFaster(tc.n); !reflect.DeepEqual(result, tc.expected) {
+			t.Errorf("Expected %v, got %v", tc.expected, result)
+		}
+	}
+}
+
+func TestRegularNumbersFasterBadInput(t *testing.T) {
+	defer func() {
+		if err := recover(); err == nil {
+			t.Errorf("Expected a panic for a negative input")
+		}
+	}()
+	RegularNumbersFaster(-2)
+}
+
+func BenchmarkRegularNumbersFaster(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			RegularNumbersFaster(tc.n)
+		}
+	}
+}
+
+func TestRegularNumbersBrute(t *testing.T) {
+	t.Parallel()
+	for _, tc := range testcases {
+		if result := RegularNumbersBrute(tc.n); !reflect.DeepEqual(result, tc.expected) {
+			t.Errorf("Expected %v, got %v", tc.expected, result)
+		}
+	}
+}
+
+func TestRegularNumbersBruteBadInput(t *testing.T) {
+	defer func() {
+		if err := recover(); err == nil {
+			t.Errorf("Expected a panic for a negative input")
+		}
+	}()
+	RegularNumbersBrute(-2)
+}
+
+func BenchmarkRegularNumbersBrute(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			RegularNumbersBrute(tc.n)
+		}
+	}
+}