Merge cf7e397 into 7519b54

README.md

@@ -45,6 +45,7 @@ problems from
 * [Day 30](https://github.com/vaskoz/dailycodingproblem-go/issues/69)
 * [Day 31](https://github.com/vaskoz/dailycodingproblem-go/issues/71)
 * [Day 33](https://github.com/vaskoz/dailycodingproblem-go/issues/73)
+* [Day 34](https://github.com/vaskoz/dailycodingproblem-go/issues/76)
 * [Day 35](https://github.com/vaskoz/dailycodingproblem-go/issues/77)
 * [Day 36](https://github.com/vaskoz/dailycodingproblem-go/issues/79)
 * [Day 37](https://github.com/vaskoz/dailycodingproblem-go/issues/81)

day34/problem.go

@@ -0,0 +1,49 @@
+package day34
+
+// MakePalindrome calculates the minimum number of insertions to make a string a palindrome.
+// Runs in O(N) time and O(N) extra space for favorLeft and favorRight.
+func MakePalindrome(str string) string {
+	letters := []rune(str)
+	favorLeft := make([]rune, len(letters))
+	copy(favorLeft, letters)
+	favorRight := make([]rune, len(letters))
+	copy(favorRight, letters)
+	left, right := 0, len(favorLeft)-1
+	for left < right {
+		if favorLeft[left] != favorLeft[right] {
+			// insert the left character on the right side
+			favorLeft = append(favorLeft, 'x')
+			copy(favorLeft[right+2:], favorLeft[right+1:])
+			favorLeft[right+1] = favorLeft[left]
+			right++
+		}
+		left++
+		right--
+	}
+	left, right = 0, len(favorRight)-1
+	for left < right {
+		if favorRight[left] != favorRight[right] {
+			// insert the right character on the left side
+			favorRight = append(favorRight, 'x')
+			copy(favorRight[left+1:], favorRight[left:])
+			favorRight[left] = favorRight[right+1]
+			right++
+		}
+		left++
+		right--
+	}
+	return chooseResult(favorLeft, favorRight)
+}
+
+func chooseResult(left, right []rune) string {
+	if len(left) < len(right) {
+		return string(left)
+	} else if len(left) == len(right) {
+		if left[0] < right[0] {
+			return string(left)
+		}
+		return string(right)
+	} else {
+		return string(right)
+	}
+}

day34/problem_test.go

@@ -0,0 +1,30 @@
+package day34
+
+import "testing"
+
+var testcases = []struct {
+	input, expected string
+}{
+	{"race", "ecarace"},
+	{"google", "elgoogle"},
+	{"add", "adda"},
+	{"caoobac", "caboobac"},
+	{"abc", "abcba"},
+}
+
+func TestMakePalindrome(t *testing.T) {
+	t.Parallel()
+	for _, tc := range testcases {
+		if result := MakePalindrome(tc.input); result != tc.expected {
+			t.Errorf("Expected %v got %v", tc.expected, result)
+		}
+	}
+}
+
+func BenchmarkMakePalindrome(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range testcases {
+			MakePalindrome(tc.input)
+		}
+	}
+}