add 2544

fishercoder1534 · fishercoder1534 · commit 3d79d0e55e1f · 2023-01-22T08:16:29.000-08:00
diff --git a/README.md b/README.md
@@ -8,6 +8,7 @@ _If you like this project, please leave me a star._ &#9733;
 
 | #    |      Title     | Solutions                                                                                                                                | Video                                                                         | Difficulty                       | Tag                  
 |------|----------------|------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------|----------------------------------|-------------
+| 2544 |[Alternating Digit Sum](https://leetcode.com/problems/alternating-digit-sum/)| [Java](../master/src/main/java/com/fishercoder/solutions/_2544.java)                                                                     || Easy                                                                          |
 | 2540 |[Minimum Common Value](https://leetcode.com/problems/minimum-common-value/)| [Java](../master/src/main/java/com/fishercoder/solutions/_2540.java)                                                                     || Easy                                                                          |
 | 2536 |[Increment Submatrices by One](https://leetcode.com/problems/increment-submatrices-by-one/)| [Java](../master/src/main/java/com/fishercoder/solutions/_2536.java)                                                                     || Medium                                                                        |
 | 2535 |[Difference Between Element Sum and Digit Sum of an Array](https://leetcode.com/problems/difference-between-element-sum-and-digit-sum-of-an-array/)| [Java](../master/src/main/java/com/fishercoder/solutions/_2535.java)                                                                     || Easy                                                                          |
diff --git a/src/main/java/com/fishercoder/solutions/_2544.java b/src/main/java/com/fishercoder/solutions/_2544.java
@@ -0,0 +1,27 @@
+package com.fishercoder.solutions;
+
+public class _2544 {
+    public static class Solution1 {
+        public int alternateDigitSum(int n) {
+            int result = 0;
+            int original = n;
+            int digits = 0;
+            while (n != 0) {
+                n /= 10;
+                digits++;
+            }
+            boolean plus = digits % 2 != 0;
+            while (original != 0) {
+                int lastDigit = original % 10;
+                if (plus) {
+                    result += lastDigit;
+                } else {
+                    result -= lastDigit;
+                }
+                plus = !plus;
+                original /= 10;
+            }
+            return result;
+        }
+    }
+}
diff --git a/src/test/java/com/fishercoder/_2544Test.java b/src/test/java/com/fishercoder/_2544Test.java
@@ -0,0 +1,27 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._2544;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class _2544Test {
+    private static _2544.Solution1 solution1;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _2544.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        assertEquals(4, solution1.alternateDigitSum(521));
+    }
+
+    @Test
+    public void test2() {
+        assertEquals(1, solution1.alternateDigitSum(10));
+    }
+
+}
