Create Manacher.java

Author: Abhinavagarwa

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

@@ -0,0 +1,45 @@
+public class ManacherAlgorithm {
+    private String preprocess(String s) {
+        StringBuilder sb = new StringBuilder();
+        sb.append('^');
+        for (int i = 0; i < s.length(); i++) {
+            sb.append('#');
+            sb.append(s.charAt(i));
+        }
+        sb.append("#$");
+        return sb.toString();
+    }
+    public String longestPalindrome(String s) {
+        String T = preprocess(s);
+        int n = T.length();
+        int[] P = new int[n];
+        int C = 0, R = 0; 
+        for (int i = 1; i < n - 1; i++) {
+            int mirror = 2 * C - i; 
+            P[i] = (R > i) ? Math.min(R - i, P[mirror]) : 0;
+            while (T.charAt(i + 1 + P[i]) == T.charAt(i - 1 - P[i])) {
+                P[i]++;
+      }
+            if (i + P[i] > R) {
+                C = i;
+                R = i + P[i];
+            }
+        }
+        int maxLen = 0;
+        int centerIndex = 0;
+        for (int i = 1; i < n - 1; i++) {
+            if (P[i] > maxLen) {
+                maxLen = P[i];
+                centerIndex = i;
+            }
+        }
+        int start = (centerIndex - maxLen) / 2;
+        return s.substring(start, start + maxLen);
+    }
+
+    public static void main(String[] args) {
+        ManacherAlgorithm ma = new ManacherAlgorithm();
+        String input = "babad";
+        System.out.println("Longest Palindromic Substring: " + ma.longestPalindrome(input));
+    }
+}