Added full code of Longest substring to form a Palindrome

Author: ujjawalsinghsde

Code Practice/Longest substring to form a Palindrome/Readme.md

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+## Longest substring to form a Palindrome
+Given a string S which only contains lowercase alphabets. Find the length of the longest substring of S such that the characters in it can be rearranged to form a palindrome. [🔗Goto](https://practice.geeksforgeeks.org/problems/longest-substring-whose-character-rearranged-can-form-a-palindrome/1#) 
+
+```Example 1:
+
+Input:
+S = "aabe"
+Output:
+3
+Explanation:
+The substring "aab" can be rearranged to
+"aba" which is the longest palindrome
+possible for this String.
+
+Example 2:
+Input:
+S = "adbabd"
+Output:
+6
+Explanation:
+The whole string “adbabd” can be
+rearranged to form a palindromic substring.
+One possible arrangement is "abddba".
+Thus, output length of the string is 6. 
+
+```
+<details>
+<summary>Full Code</summary>
+
+```java
+import java.io.*;
+import java.util.*;
+
+class GFG {
+    public static void main(String args[]) throws IOException {
+        BufferedReader read =
+            new BufferedReader(new InputStreamReader(System.in));
+        int t = Integer.parseInt(read.readLine());
+        while (t-- > 0) {
+            String S = read.readLine();
+            
+            Solution ob = new Solution();
+            System.out.println(ob.longestSubstring(S));
+        }
+    }
+}// } Driver Code Ends
+
+
+//User function Template for Java
+
+class Solution {
+    static int longestSubstring(String s) {
+        HashMap<Integer, Integer> index = new HashMap<>();
+
+        int answer = 0;
+
+        int mask = 0;
+        index.put(mask, -1);
+
+        for (int i = 0; i < s.length(); i++) {
+
+            int temp = (int) s.charAt(i) - 'a';
+
+            mask ^= (1 << temp);
+
+            if (index.containsKey(mask)) {
+                answer = Math.max(answer, i - index.get(mask));
+            } else {
+                index.put(mask, i);
+            }
+
+            for (int j = 0; j < 26; j++) {
+                int mask2 = mask ^ (1 << j);
+                if (index.containsKey(mask2)) {
+                    answer = Math.max(answer, i - index.get(mask2));
+                }
+            }
+        }
+        return answer;
+    }
+};
+```
+</details>
+
+```java
+class Solution {
+    static int longestSubstring(String s) {
+        HashMap<Integer, Integer> index = new HashMap<>();
+
+        int answer = 0;
+
+        int mask = 0;
+        index.put(mask, -1);
+
+        for (int i = 0; i < s.length(); i++) {
+
+            int temp = (int) s.charAt(i) - 'a';
+
+            mask ^= (1 << temp);
+
+            if (index.containsKey(mask)) {
+                answer = Math.max(answer, i - index.get(mask));
+            } else {
+                index.put(mask, i);
+            }
+
+            for (int j = 0; j < 26; j++) {
+                int mask2 = mask ^ (1 << j);
+                if (index.containsKey(mask2)) {
+                    answer = Math.max(answer, i - index.get(mask2));
+                }
+            }
+        }
+        return answer;
+    }
+};
+```