feat: Manacher's algorithm (#408)

strings/manacher/longestpalindrome.go

@@ -0,0 +1,63 @@
+// longestpalindrome.go
+// description: Manacher's algorithm (Longest palindromic substring)
+// details:
+// An algorithm with linear running time that allows you to get compressed information about all palindromic substrings of a given string. - [Manacher's algorithm](https://en.wikipedia.org/wiki/Longest_palindromic_substring)
+// author(s) [red_byte](https://github.com/i-redbyte)
+// see longestpalindrome_test.go
+
+package manacher
+
+import (
+	"github.com/TheAlgorithms/Go/math/min"
+	"strings"
+)
+
+func makeBoundaries(s string) string {
+	var result strings.Builder
+	result.WriteRune('#')
+	for _, ch := range s {
+		if ch != ' ' { //ignore space as palindrome character
+			result.WriteRune(ch)
+		}
+		result.WriteRune('#')
+	}
+	return result.String()
+}
+
+func nextBoundary(s string) string {
+	var result strings.Builder
+	for _, ch := range s {
+		if ch != '#' {
+			result.WriteRune(ch)
+		}
+	}
+	return result.String()
+}
+
+func LongestPalindrome(s string) string {
+	boundaries := makeBoundaries(s)
+	b := make([]int, len(boundaries))
+	k := 0
+	index := 0
+	maxLen := 0
+	maxCenterSize := 0
+	for i := range b {
+		if i < k {
+			b[i] = min.Int(b[2*index-i], k-i)
+		} else {
+			b[i] = 1
+		}
+		for i-b[i] >= 0 && i+b[i] < len(boundaries) && boundaries[i-b[i]] == boundaries[i+b[i]] {
+			b[i] += 1
+		}
+		if maxLen < b[i]-1 {
+			maxLen = b[i] - 1
+			maxCenterSize = i
+		}
+		if b[i]+i-1 > k {
+			k = b[i] + i - 1
+			index = i
+		}
+	}
+	return nextBoundary(boundaries[maxCenterSize-maxLen : maxCenterSize+maxLen])
+}

strings/manacher/longestpalindrome_test.go

@@ -0,0 +1,38 @@
+// longestpalindrome_test.go
+// description: Manacher's algorithm (Longest palindromic substring)
+// author(s) [red_byte](https://github.com/i-redbyte)
+// see longestpalindrome.go
+
+package manacher
+
+import "testing"
+
+func getTests() []struct {
+	s      string
+	result string
+} {
+	var tests = []struct {
+		s      string
+		result string
+	}{
+		{"olokazakabba", "kazak"},
+		{"abaacakkkkk", "kkkkk"},
+		{"qqqq C++ groovy mom pooop", "pooop"},
+		{"CCCPCCC @@@ hello", "CCCPCCC"},
+		{"goog gogogogogog -go- gogogogo ", "gogogogogog"},
+	}
+	return tests
+}
+
+func TestLongestPalindrome(t *testing.T) {
+	tests := getTests()
+	for _, tv := range tests {
+		t.Run(tv.s, func(t *testing.T) {
+			result := LongestPalindrome(tv.s)
+			t.Log(tv.s, " ", result)
+			if result != tv.result {
+				t.Errorf("Wrong result! Expected:%s, returned:%s ", tv.result, result)
+			}
+		})
+	}
+}