solves #2544: Alternating Digit Sum in java

Author: anishLearnsToCode

README.md

@@ -796,7 +796,7 @@
 | 2529 | [Maximum Count of Positive Integer and Negative Integer](https://leetcode.com/problems/maximum-count-of-positive-integer-and-negative-integer)                         |                                                                       [![Java](assets/java.png)](src/MaximumCountOfPositiveIntegerAndNegativeInteger.java)                                                                       |                                                                                                                                   |
 | 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](assets/java.png)](src/DifferenceBetweenElementSumAndDigitSumOfAnArray.java)                                                                       |                                                                                                                                   |
 | 2540 | [Minimum Common Value](https://leetcode.com/problems/minimum-common-value)                                                                                             |                                                                                     [![Java](assets/java.png)](src/MinimumCommonValue.java)                                                                                      |                                                                                                                                   |
-| 2544 | [Alternating Digit Sum](https://leetcode.com/problems/alternating-digit-sum)                                                                                           |                                                                                                                                                                                                                                  |                                                                                                                                   |
+| 2544 | [Alternating Digit Sum](https://leetcode.com/problems/alternating-digit-sum)                                                                                           |                                                                                     [![Java](assets/java.png)](src/AlternatingDigitSum.java)                                                                                     |                                                                                                                                   |
 | 2549 | [Count Distinct Numbers on Board](https://leetcode.com/problems/count-distinct-numbers-on-board)                                                                       |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 2553 | [Separate the Digits in an Array](https://leetcode.com/problems/separate-the-digits-in-an-array)                                                                       |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 2558 | [Take Gifts From the Richest Pile](https://leetcode.com/problems/take-gifts-from-the-richest-pile)                                                                     |                                                                                                                                                                                                                                  |                                                                                                                                   |

src/AlternatingDigitSum.java

@@ -0,0 +1,14 @@
+// https://leetcode.com/problems/alternating-digit-sum
+// T: O(log(n))
+// S: O(1)
+
+public class AlternatingDigitSum {
+    public int alternateDigitSum(int n) {
+        final String number = n + "";
+        int sum = 0;
+        for (int index = 0, parity = 1 ; index < number.length() ; index++, parity *= -1) {
+            sum += parity * (number.charAt(index) - '0');
+        }
+        return sum;
+    }
+}