add 2243

Author: fishercoder1534

README.md

@@ -8,6 +8,7 @@ _If you like this project, please leave me a star._ ★
 
 | #    |      Title     | Solutions                                                                                                                                | Video                                                                         | Difficulty  | Tag                  
 |------|----------------|------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------|-------------|-------------
+| 2243 |[Calculate Digit Sum of a String](https://leetcode.com/problems/calculate-digit-sum-of-a-string/)| [Java](../master/src/main/java/com/fishercoder/solutions/_2243.java)                                                                      || Easy                                                                          ||
 | 2220 |[Minimum Bit Flips to Convert Number](https://leetcode.com/problems/minimum-bit-flips-to-convert-number/)| [Java](../master/src/main/java/com/fishercoder/solutions/_2220.java)                                                                     || Easy                                                                          ||
 | 2215 |[Find the Difference of Two Arrays](https://leetcode.com/problems/find-the-difference-of-two-arrays/)| [Java](../master/src/main/java/com/fishercoder/solutions/_2215.java)                                                                     || Easy                                                                          ||
 | 2210 |[Count Hills and Valleys in an Array](https://leetcode.com/problems/count-hills-and-valleys-in-an-array/)| [Java](../master/src/main/java/com/fishercoder/solutions/_2210.java)                                                                     || Easy                                                                          ||

src/main/java/com/fishercoder/solutions/_2243.java

@@ -0,0 +1,21 @@
+package com.fishercoder.solutions;
+
+public class _2243 {
+    public static class Solution1 {
+        public String digitSum(String s, int k) {
+            StringBuilder sb = new StringBuilder();
+            while (s.length() > k) {
+                for (int i = 0; i < s.length(); i += k) {
+                    int sum = 0;
+                    for (int j = i; j < i + k && j < s.length(); j++) {
+                        sum += Integer.parseInt(s.charAt(j) + "");
+                    }
+                    sb.append(sum);
+                }
+                s = sb.toString();
+                sb.setLength(0);
+            }
+            return s;
+        }
+    }
+}