cs: add «443. String Compression»

Signed-off-by: Matej Focko <me@mfocko.xyz>

cs/string-compression.cs

@@ -0,0 +1,33 @@
+public class Solution {
+    private static int WriteChar(char[] chars, int start, char c, int count) {
+        chars[start++] = c;
+        if (count == 1) {
+            return start;
+        }
+
+        int digits = 1 + (int)Math.Log10(count);
+
+        start += digits - 1;
+        for (int offset = 0; offset < digits; count /= 10, ++offset) {
+            chars[start - offset] = (char)('0' + (count % 10));
+        }
+
+        return start + 1;
+    }
+
+    public int Compress(char[] chars) {
+        int i = 0;
+
+        var count = 1;
+        for (int j = 1; j < chars.Length; ++j) {
+            if (chars[j] != chars[j - 1]) {
+                i = WriteChar(chars, i, chars[j - 1], count);
+                count = 0;
+            }
+
+            ++count;
+        }
+
+        return WriteChar(chars, i, chars.Last(), count);
+    }
+}