solves #2180: Count Integers With Even Digit Sum in java

Author: anishLearnsToCode

README.md

@@ -707,7 +707,7 @@
 | 2129 | [Capitalize the Title](https://leetcode.com/problems/capitalize-the-title)                                                                                             |                                                                                     [![Java](assets/java.png)](src/CapitalizeTheTitle.java)                                                                                      |                                                                                                                                   |
 | 2133 | [Check if Every Row and Column Contains All Numbers](https://leetcode.com/problems/check-if-every-row-and-column-contains-all-numbers)                                 |                                                                       [![Java](assets/java.png)](src/CheckIfEveryRowAndEveryColumnContainAllNumbers.java)                                                                        |                                                                                                                                   |
 | 2138 | [Divide a String Into Groups of Size k](https://leetcode.com/problems/divide-a-string-into-groups-of-size-k)                                                           |                                                                              [![Java](assets/java.png)](src/DivideTheStringIntoGroupsOfSizeK.java)                                                                               |                                                                                                                                   |
-| 2144 | [Minimum Cost of Buying Candies With Discount](https://leetcode.com/problems/minimum-cost-of-buying-candies-with-discount)                                             |                                                                                                                                                                                                                                  |                                                                                                                                   |
+| 2144 | [Minimum Cost of Buying Candies With Discount](https://leetcode.com/problems/minimum-cost-of-buying-candies-with-discount)                                             |                                                                                [![Java](assets/java.png)](src/CountIntegersWithEvenDigitSum.java)                                                                                |                                                                                                                                   |
 | 2148 | [Count Elements With Strictly Smaller and Greater Elements](https://leetcode.com/problems/count-elements-with-strictly-smaller-and-greater-elements)                   |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 2154 | [Keep Multiplying Found Values by Two](https://leetcode.com/problems/keep-multiplying-found-values-by-two)                                                             |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 2160 | [Minimum Sum of Four Digit Number After Splitting Digits](https://leetcode.com/problems/minimum-sum-of-four-digit-number-after-splitting-digits)                       |                                                                                                                                                                                                                                  |                                                                                                                                   |

src/CountIntegersWithEvenDigitSum.java

@@ -0,0 +1,14 @@
+// https://leetcode.com/problems/count-integers-with-even-digit-sum
+// T: O(1)
+// S: O(1)
+
+public class CountIntegersWithEvenDigitSum {
+    public int countEven(int num) {
+        final int group = num / 10;
+        return 5 * group - 1 + (num % 10 + 1 + series(group)) / 2;
+    }
+
+    private int series(int group) {
+        return (group % 10 + (group % 100) / 10 + (group % 1000) / 100 + 1) % 2;
+    }
+}