Merge e07ca0f into fc6f83b

README.md

@@ -247,4 +247,5 @@ problems from
 * [Day 236](https://github.com/vaskoz/dailycodingproblem-go/issues/485)
 * [Day 237](https://github.com/vaskoz/dailycodingproblem-go/issues/487)
 * [Day 238](https://github.com/vaskoz/dailycodingproblem-go/issues/489)
+* [Day 240](https://github.com/vaskoz/dailycodingproblem-go/issues/492)
 * [Day 241](https://github.com/vaskoz/dailycodingproblem-go/issues/493)

day240/problem.go

@@ -0,0 +1,46 @@
+package day240
+
+// MinSwapsAdjacentPairs returns the minimum number of swaps
+// required to bring all pairs together.
+// A pair consists of the same value.
+// Invalid input results in a panic.
+func MinSwapsAdjacentPairs(pairs []int) int {
+	if len(pairs)%2 != 0 {
+		panic("must even number of inputs")
+	}
+	indicies := make(map[int][]int, len(pairs)/2)
+	for i, id := range pairs {
+		indicies[id] = append(indicies[id], i)
+	}
+	if len(indicies) != len(pairs)/2 {
+		panic("invalid pair data")
+	}
+	for _, pos := range indicies {
+		if len(pos) != 2 {
+			panic("all values must be pairs")
+		}
+	}
+	return minSwapsAdjacentPairs(pairs, indicies, 0)
+}
+
+func minSwapsAdjacentPairs(pairs []int, indicies map[int][]int, pos int) int {
+	if pos == len(pairs) {
+		return 0
+	}
+	firstIndex := pos
+	secondIndex := pos + 1
+	first := pairs[firstIndex]
+	second := pairs[secondIndex]
+	if first == second {
+		return minSwapsAdjacentPairs(pairs, indicies, pos+2)
+	}
+	min := int(^uint(0) >> 1)
+	// NOTE: It doesn't matter which one you swap due to symmetry.
+	swapWithSecond := indicies[first][1]
+	pairs[secondIndex], pairs[swapWithSecond] = pairs[swapWithSecond], pairs[secondIndex]
+	if minBelow := 1 + minSwapsAdjacentPairs(pairs, indicies, pos+2); min > minBelow {
+		min = minBelow
+	}
+	pairs[secondIndex], pairs[swapWithSecond] = pairs[swapWithSecond], pairs[secondIndex]
+	return min
+}

day240/problem_test.go

@@ -0,0 +1,70 @@
+package day240
+
+import "testing"
+
+var testcases = []struct {
+	pairs    []int
+	minSwaps int
+}{
+	{[]int{0, 2, 1, 2, 0, 1}, 2},
+	{[]int{0, 3, 1, 1, 2, 2, 3, 0}, 1},
+	{[]int{0, 3, 2, 3, 0, 2}, 2},
+	{[]int{1, 2, 3, 3, 1, 2}, 1},
+	{[]int{3, 2, 3, 1, 1, 2}, 2},
+	{[]int{0, 3, 0, 2, 3, 2}, 2},
+	{[]int{0, 3, 2, 3, 0, 2}, 2},
+}
+
+func TestMinSwapsAdjacentPairs(t *testing.T) {
+	t.Parallel()
+	for _, tc := range testcases {
+		copied := make([]int, len(tc.pairs))
+		copy(copied, tc.pairs)
+		if result := MinSwapsAdjacentPairs(copied); result != tc.minSwaps {
+			t.Errorf("Expected %v, got %v", tc.minSwaps, result)
+		}
+	}
+}
+
+func TestMinSwapsAdjacentPairsNotEventInput(t *testing.T) {
+	t.Parallel()
+	defer func() {
+		if err := recover(); err == nil {
+			t.Errorf("Expected an error for odd number of pairs")
+		}
+	}()
+	pairs := []int{1, 1, 1}
+	MinSwapsAdjacentPairs(pairs)
+}
+
+func TestMinSwapsAdjacentPairsMoreThanTwoInPair(t *testing.T) {
+	t.Parallel()
+	defer func() {
+		if err := recover(); err == nil {
+			t.Errorf("Expected an error if there are more than 2 in a pair")
+		}
+	}()
+	pairs := []int{1, 1, 1, 1}
+	MinSwapsAdjacentPairs(pairs)
+}
+
+func TestMinSwapsAdjacentPairsThreeInPair(t *testing.T) {
+	t.Parallel()
+	defer func() {
+		if err := recover(); err == nil {
+			t.Errorf("Expected an error if there are more than 2 in a pair")
+		}
+	}()
+	pairs := []int{3, 2, 3, 3, 1, 1}
+	MinSwapsAdjacentPairs(pairs)
+}
+
+func BenchmarkMinSwapsAdjacentPairs(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			copied := make([]int, len(tc.pairs))
+			copy(copied, tc.pairs)
+			MinSwapsAdjacentPairs(copied)
+		}
+	}
+}