add 2351

Author: fishercoder1534

README.md

@@ -8,6 +8,7 @@ _If you like this project, please leave me a star._ ★
 
 | #    |      Title     | Solutions                                                                                                                                | Video                                                                         | Difficulty                       | Tag                  
 |------|----------------|------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------|----------------------------------|-------------
+| 2351 |[First Letter to Appear Twice](https://leetcode.com/problems/first-letter-to-appear-twice/)| [Java](../master/src/main/java/com/fishercoder/solutions/_2351.java)                                                                      || Easy                                                                             ||
 | 2347 |[Maximum Number of Pairs in Array](https://leetcode.com/problems/best-poker-hand/)| [Java](../master/src/main/java/com/fishercoder/solutions/_2347.java)                                                                     || Easy                                                                             ||
 | 2341 |[Maximum Number of Pairs in Array](https://leetcode.com/problems/maximum-number-of-pairs-in-array/)| [Java](../master/src/main/java/com/fishercoder/solutions/_2341.java)                                                                     || Easy                                                                             ||
 | 2335 |[Minimum Amount of Time to Fill Cups](https://leetcode.com/problems/minimum-amount-of-time-to-fill-cups/)| [Java](../master/src/main/java/com/fishercoder/solutions/_2335.java)                                                                     || Easy                                                                             ||

src/main/java/com/fishercoder/solutions/_2351.java

@@ -0,0 +1,18 @@
+package com.fishercoder.solutions;
+
+import java.util.HashSet;
+import java.util.Set;
+
+public class _2351 {
+    public static class Solution1 {
+        public char repeatedCharacter(String s) {
+            Set<Character> set = new HashSet<>();
+            for (char c : s.toCharArray()) {
+                if (!set.add(c)) {
+                    return c;
+                }
+            }
+            return ' ';
+        }
+    }
+}