add 2309

Author: fishercoder1534

README.md

@@ -8,6 +8,7 @@ _If you like this project, please leave me a star._ ★
 
 | #    |      Title     | Solutions                                                                                                                                | Video                                                                         | Difficulty  | Tag                  
 |------|----------------|------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------|-------------|-------------
+| 2309 |[Greatest English Letter in Upper and Lower Case](https://leetcode.com/problems/greatest-english-letter-in-upper-and-lower-case/)| [Java](../master/src/main/java/com/fishercoder/solutions/_2309.java)                                                                     || Easy                                                                             ||
 | 2299 |[Strong Password Checker II](https://leetcode.com/problems/strong-password-checker-ii/)| [Java](../master/src/main/java/com/fishercoder/solutions/_2299.java)                                                                     || Easy                                                                             ||
 | 2288 |[Apply Discount to Prices](https://leetcode.com/problems/apply-discount-to-prices/)| [Java](../master/src/main/java/com/fishercoder/solutions/_2288.java)                                                                     || Medium                                                                        ||
 | 2287 |[Rearrange Characters to Make Target String](https://leetcode.com/problems/rearrange-characters-to-make-target-string/)| [Java](../master/src/main/java/com/fishercoder/solutions/_2288.java)                                                                     || Easy                                                                          ||

src/main/java/com/fishercoder/solutions/_2309.java

@@ -0,0 +1,31 @@
+package com.fishercoder.solutions;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+public class _2309 {
+    public static class Solution1 {
+        public String greatestLetter(String s) {
+            List<Character> lowercase = new ArrayList<>();
+            List<Character> uppercase = new ArrayList<>();
+            for (char c : s.toCharArray()) {
+                if (Character.isLowerCase(c)) {
+                    lowercase.add(c);
+                } else {
+                    uppercase.add(c);
+                }
+            }
+            Collections.sort(uppercase, Collections.reverseOrder());
+            Collections.sort(lowercase, Collections.reverseOrder());
+            for (int i = 0; i < uppercase.size(); i++) {
+                for (int j = 0; j < lowercase.size(); j++) {
+                    if (Character.toLowerCase(uppercase.get(i)) == lowercase.get(j)) {
+                        return uppercase.get(i) + "";
+                    }
+                }
+            }
+            return "";
+        }
+    }
+}

src/test/java/com/fishercoder/_2309Test.java

@@ -0,0 +1,27 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._2309;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class _2309Test {
+    private static _2309.Solution1 solution1;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _2309.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        assertEquals("E", solution1.greatestLetter("lEeTcOdE"));
+    }
+
+    @Test
+    public void test2() {
+        assertEquals("R", solution1.greatestLetter("arRAzFif"));
+    }
+
+}