Add / Longest palindromic substring

Author: SagarGaniga

DP/Longest Palindrome Substring/LPS.java

@@ -0,0 +1,79 @@
+// Longest palindromic substring
+// Manacher's algorithm
+
+import java.util.Arrays;
+
+class LPS{
+
+    static void printSubStr(String str, int low, int high) { 
+        System.out.println(str.substring(low, high + 1)); 
+    } 
+
+    public static void main(String[] args) { 
+        String str = "abcdcbaf"; 
+        System.out.println("Length is: " +  
+                                 longestPalSubstr(str)); 
+    } 
+
+    // input string
+    static int longestPalSubstr(String str){
+
+        // Get the length
+        int n = str.length();
+
+        // make a table of length * length
+        boolean table[][] = new boolean[n][n];
+
+        // single letter is always palindrome 
+        // Lol
+        // make max = 1
+        int maxLength = 1;
+        
+        // and fill the diagonals as 1 as true
+        for (int i = 0; i < n; ++i) 
+            table[i][i] = true;
+
+        
+        // for strings with length 2
+        int start = 0;
+
+        // go ot n-1
+        for(int i = 0; i< n-1; i++){
+            
+            // this and immidiate next
+            if(str.charAt(i) == str.charAt(i+1)){
+                // if matched make it true
+                // i and i+1
+                table[i][i+1] = true;
+                
+                // this is palindrome and hence update the start and maxlength
+                start = i;
+                maxLength = 2;
+            }
+        }
+
+
+        // Now for 3 and more
+        // we will use 1 and 2 data from table
+        for(int k = 3; k <=  n; k++){
+            for(int i = 0; i < n-k+1; i++){
+                int j = i + k - 1;
+                if(table[i+1][j-1] && str.charAt(i) == str.charAt(j)){
+                    table[i][j] = true;
+
+                    if(k > maxLength){
+                        start = i;
+                        maxLength = k;
+                    }
+                }
+            }
+        }
+
+        System.out.print("Longest palindrome substring is; "); 
+        printSubStr(str, start, start + maxLength - 1); 
+          
+        return maxLength; // return length of LPS 
+        
+    }
+
+}