Create Longest Palindrome.java

Author: Lokesh598

String/Longest Palindrome.java

@@ -0,0 +1,30 @@
+class Solution {
+
+    public int longestPalindrome(String s) {
+        // Map to store frequency of occurrence of each character
+        Map<Character, Integer> frequencyMap = new HashMap<>();
+        // Count frequencies
+        for (char c : s.toCharArray()) {
+            frequencyMap.put(c, frequencyMap.getOrDefault(c, 0) + 1);
+        }
+
+        int res = 0;
+        boolean hasOddFrequency = false;
+        for (int freq : frequencyMap.values()) {
+            // Check is the frequency is even
+            if ((freq % 2) == 0) {
+                res += freq;
+            } else {
+                // If the frequency is odd, one occurrence of the
+                // character will remain without a match
+                res += freq - 1;
+                hasOddFrequency = true;
+            }
+        }
+        // If hasOddFrequency is true, we have at least one unmatched
+        // character to make the center of an odd length palindrome.
+        if (hasOddFrequency) return res + 1;
+
+        return res;
+    }
+}