Merge pull request #930 from vaskoz/day460

Day460

README.md

@@ -457,4 +457,5 @@ problems from
 * [Day 457](https://github.com/vaskoz/dailycodingproblem-go/issues/923)
 * [Day 458](https://github.com/vaskoz/dailycodingproblem-go/issues/925)
 * [Day 459](https://github.com/vaskoz/dailycodingproblem-go/issues/927)
+* [Day 460](https://github.com/vaskoz/dailycodingproblem-go/issues/929)
 

day460/problem.go

@@ -0,0 +1,35 @@
+package day460
+
+// FlipsXsBeforeYs returns the minimum number of flips
+// required to meet the condition that the result should
+// have all X's before Y's.
+// Runs in O(N) time and O(1) space.
+func FlipsXsBeforeYs(input string) int {
+	streakX, streakY := true, true
+
+	var changeXtoY, changeYtoX int
+
+	for forward, backward := 0, len(input)-1; forward < len(input); forward, backward = forward+1, backward-1 {
+		if streakX && input[forward] != 'x' {
+			streakX = false
+		}
+
+		if streakY && input[backward] != 'y' {
+			streakY = false
+		}
+
+		if !streakX && input[forward] == 'x' {
+			changeXtoY++
+		}
+
+		if !streakY && input[backward] == 'y' {
+			changeYtoX++
+		}
+	}
+
+	if changeXtoY < changeYtoX {
+		return changeXtoY
+	}
+
+	return changeYtoX
+}

day460/problem_test.go

@@ -0,0 +1,38 @@
+package day460
+
+import "testing"
+
+// nolint
+var testcases = []struct {
+	input string
+	flips int
+}{
+	{"xyxxxyxyy", 2},
+	{"yxxyyyy", 1},
+	{"yyyxy", 1},
+	{"yxyxyx", 3},
+	{"yyyyxyyyxyyyyxx", 4},
+	{"xxxxxxx", 0},
+	{"yyyyyyyyyy", 0},
+	{"xyyyyyyyy", 0},
+	{"xxxxxxxxyyy", 0},
+	{"xxxyyxxyyxxyyyyyyyyy", 4},
+}
+
+func TestFlipsXsBeforeYs(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range testcases {
+		if flips := FlipsXsBeforeYs(tc.input); flips != tc.flips {
+			t.Errorf("Expected %v, got %v", tc.flips, flips)
+		}
+	}
+}
+
+func BenchmarkFlipsXsBeforeYs(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			FlipsXsBeforeYs(tc.input)
+		}
+	}
+}