Created LongestPalinSubstring.java

LongestPalinSubstring.java

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+public class LongestPalinSubstring  
+{ 
+    // A utility function to print a substring str[low..high] 
+    static void printSubStr(String str, int low, int high) { 
+        System.out.println(str.substring(low, high + 1)); 
+    } 
+
+    // This function prints the longest palindrome substring 
+    // of str[]. 
+    // It also returns the length of the longest palindrome 
+    static int longestPalSubstr(String str) { 
+        int n = str.length();   // get length of input string 
+
+        // table[i][j] will be false if substring str[i..j] 
+        // is not palindrome. 
+        // Else table[i][j] will be true 
+        boolean table[][] = new boolean[n][n]; 
+
+        // All substrings of length 1 are palindromes 
+        int maxLength = 1; 
+        for (int i = 0; i < n; ++i) 
+            table[i][i] = true; 
+
+        // check for sub-string of length 2. 
+        int start = 0; 
+        for (int i = 0; i < n - 1; ++i) { 
+            if (str.charAt(i) == str.charAt(i + 1)) { 
+                table[i][i + 1] = true; 
+                start = i; 
+                maxLength = 2; 
+            } 
+        } 
+
+        // Check for lengths greater than 2. k is length 
+        // of substring 
+        for (int k = 3; k <= n; ++k) { 
+
+                  // Fix the starting index 
+            for (int i = 0; i < n - k + 1; ++i)  
+            { 
+                // Get the ending index of substring from 
+                // starting index i and length k 
+                int j = i + k - 1; 
+
+                // checking for sub-string from ith index to 
+                // jth index iff str.charAt(i+1) to  
+                // str.charAt(j-1) is a palindrome 
+                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 
+    } 
+
+    // Driver program to test above functions 
+    public static void main(String[] args) { 
+
+        String str = "dracecarf"; 
+        System.out.println("Length is: " +  
+                                 longestPalSubstr(str)); 
+    } 
+}