Merge pull request #938 from vaskoz/day463

Day463

README.md

@@ -459,6 +459,7 @@ problems from
 * [Day 459](https://github.com/vaskoz/dailycodingproblem-go/issues/927)
 * [Day 460](https://github.com/vaskoz/dailycodingproblem-go/issues/929)
 * [Day 461](https://github.com/vaskoz/dailycodingproblem-go/issues/931)
+* [Day 463](https://github.com/vaskoz/dailycodingproblem-go/issues/937)
 * [Day 464](https://github.com/vaskoz/dailycodingproblem-go/issues/935)
 * [Day 465](https://github.com/vaskoz/dailycodingproblem-go/issues/933)
 

day463/problem.go

@@ -0,0 +1,38 @@
+package day463
+
+// MinimizeQux returns the smallest Qux slice
+// possible.
+// Runs in O(N*K) where K is the number of elements that can removed.
+// Uses O(N) extra space to avoid modifying the input.
+func MinimizeQux(input []rune) []rune {
+	lastLen := 0
+	copied := make([]rune, len(input))
+	copy(copied, input)
+
+	for len(copied) != lastLen {
+		lastLen = len(copied)
+		copied = minimizeQux(copied)
+	}
+
+	return copied
+}
+
+func minimizeQux(input []rune) []rune {
+	min := input
+
+	for i := 1; i < len(input); i++ {
+		if input[i] != input[i-1] {
+			missing := 'R' + 'G' + 'B' - input[i] - input[i-1]
+			end := append([]rune{missing}, input[i+1:]...)
+			candidate := append([]rune{}, input[:i-1]...)
+			candidate = append(candidate, end...)
+			candidate = minimizeQux(candidate)
+
+			if len(candidate) < len(min) {
+				min = candidate
+			}
+		}
+	}
+
+	return min
+}

day463/problem_test.go

@@ -0,0 +1,34 @@
+package day463
+
+import (
+	"reflect"
+	"testing"
+)
+
+// nolint
+var testcases = []struct {
+	input    []rune
+	expected []rune
+}{
+	{[]rune{'R', 'G', 'B', 'G', 'B'}, []rune{'R'}},
+	{[]rune{'G', 'B', 'G', 'B'}, []rune{'B', 'B'}},
+	{[]rune{'B', 'B', 'B', 'R', 'G', 'G', 'G'}, []rune{'G', 'G'}},
+}
+
+func TestMinimizeQux(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range testcases {
+		if result := MinimizeQux(tc.input); !reflect.DeepEqual(tc.expected, result) {
+			t.Errorf("Expected %v, got %v", tc.expected, result)
+		}
+	}
+}
+
+func BenchmarkMinimizeQux(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			MinimizeQux(tc.input)
+		}
+	}
+}