FirstNonRepeatingLetter solution

src/main/java/com/algos/codewars/FirstNonRepeatingLetter.java

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+package com.algos.codewars;
+
+//Write a function named first_non_repeating_letter† that takes a string input,
+// and returns the first character that is not repeated anywhere in the string.
+//
+//        For example, if given the input 'stress', the function should return 't',
+//        since the letter t only occurs once in the string, and occurs first in the string.
+//
+//        As an added challenge, upper- and lowercase letters are considered the same character,
+//        but the function should return the correct case for the initial letter. For example, the input 'sTreSS' should return 'T'.
+//
+//        If a string contains all repeating characters, it should return an empty string ("");
+//
+//        † Note: the function is called firstNonRepeatingLetter for historical reasons,
+//        but your function should handle any Unicode character.
+
+
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+public class FirstNonRepeatingLetter {
+
+    public static void main(String[] args) {
+        System.out.println(firstNonRepeatingLetter("manOn-aMoon"));
+    }
+
+    public static String firstNonRepeatingLetter(String s) {
+
+        if (s == null || s.isEmpty()) {
+            return "";
+        }
+
+        Map<Character, Integer> charCount = new LinkedHashMap<>();
+        for (int i = 0; i < s.length(); i++) {
+            char c = Character.toLowerCase(s.charAt(i));
+            charCount.merge(c, 1, Integer::sum);
+        }
+
+        for (int i = 0; i < s.length(); i++) {
+            char currentChar = s.charAt(i);
+            if (charCount.get(Character.toLowerCase(currentChar)) == 1) {
+                return String.valueOf(currentChar);
+            }
+        }
+
+        return "";
+
+//     List<String> c = s.toLowerCase().chars().mapToObj(ch -> (char) ch).map(String::valueOf).toList();
+
+//     for (int i = 0; i < s.length(); i++) {
+//       if (Collections.frequency(c, c.get(i).toLowerCase()) == 1) {
+//         return String.valueOf(s.charAt(i));
+//       }
+//     }
+//        return "";
+    }
+}