Create Manacher.java

DIRECTORY.md

@@ -560,6 +560,7 @@
             * [LongestNonRepetitiveSubstring](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/LongestNonRepetitiveSubstring.java)
             * [LongestPalindromicSubstring](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/LongestPalindromicSubstring.java)
             * [Lower](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/Lower.java)
+            * [Manacher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/Manacher.java)
             * [MyAtoi](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/MyAtoi.java)
             * [Palindrome](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/Palindrome.java)
             * [Pangram](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/strings/Pangram.java)
@@ -846,6 +847,8 @@
             * [TwinPrimeTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/TwinPrimeTest.java)
             * [VolumeTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/maths/VolumeTest.java)
           * misc
+            * [ColorContrastRatioTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/ColorContrastRatioTest.java)
+            * [InverseOfMatrixTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/InverseOfMatrixTest.java)
             * [MapReduceTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/MapReduceTest.java)
             * [MedianOfMatrixtest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/MedianOfMatrixtest.java)
             * [MedianOfRunningArrayTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/MedianOfRunningArrayTest.java)
@@ -857,6 +860,7 @@
             * [ArrayRightRotation](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/ArrayRightRotation.java)
             * [ArrayRightRotationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/ArrayRightRotationTest.java)
             * [BestFitCPUTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/BestFitCPUTest.java)
+            * [BFPRTTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/BFPRTTest.java)
             * [BoyerMooreTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/BoyerMooreTest.java)
             * cn
               * [HammingDistanceTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/others/cn/HammingDistanceTest.java)

src/main/java/com/thealgorithms/strings/Manacher.java

@@ -0,0 +1,56 @@
+public class ManacherAlgorithm {
+
+    // Preprocesses the input string by adding boundary characters
+    private String preprocess(String s) {
+        StringBuilder sb = new StringBuilder();
+        sb.append('^');  // Add starting boundary
+        for (int i = 0; i < s.length(); i++) {
+            sb.append('#');  // Add boundary between characters
+            sb.append(s.charAt(i));
+        }
+        sb.append("#$");  // Add ending boundary
+        return sb.toString();
+    }
+
+    // Manacher's Algorithm to find the longest palindromic substring
+    public String longestPalindrome(String s) {
+        String T = preprocess(s);
+        int n = T.length();
+        int[] P = new int[n];  // Array to store the lengths of palindromes
+        int C = 0, R = 0;  // C is the center, R is the right boundary
+
+        // Iterate through the transformed string
+        for (int i = 1; i < n - 1; i++) {
+            int mirror = 2 * C - i;  // Mirror of i with respect to the center C
+
+            // Use previously computed values or set P[i] to 0
+            P[i] = (R > i) ? Math.min(R - i, P[mirror]) : 0;
+
+            // Expand around i
+            while (T.charAt(i + 1 + P[i]) == T.charAt(i - 1 - P[i])) {
+                P[i]++;
+            }
+
+            // Update center and right boundary if the palindrome expands beyond R
+            if (i + P[i] > R) {
+                C = i;
+                R = i + P[i];
+            }
+        }
+
+        // Find the longest palindrome in P
+        int maxLen = 0;
+        int centerIndex = 0;
+        for (int i = 1; i < n - 1; i++) {
+            if (P[i] > maxLen) {
+                maxLen = P[i];
+                centerIndex = i;
+            }
+        }
+
+        // Calculate the starting index of the longest palindromic substring
+        int start = (centerIndex - maxLen) / 2;
+        return s.substring(start, start + maxLen);
+    }
+}
+