java: add «2381. Shifting Letters II»

URL:	https://leetcode.com/problems/shifting-letters-ii/
Signed-off-by: Matej Focko <me@mfocko.xyz>

java/shifting-letters-ii.java

@@ -0,0 +1,38 @@
+class Solution {
+  public String shiftingLetters(String s, int[][] shifts) {
+    var diff = new int[s.length()];
+    for (var shift : shifts) {
+      var start = shift[0];
+      var end = shift[1];
+
+      if (shift[2] == 0) {
+        --diff[start];
+
+        if (end + 1 < s.length()) {
+          ++diff[end + 1];
+        }
+      } else if (shift[2] == 1) {
+        ++diff[start];
+
+        if (end + 1 < s.length()) {
+          --diff[end + 1];
+        }
+      }
+    }
+
+    var result = new StringBuilder(s);
+
+    var shiftBy = 0;
+    for (var i = 0; i < s.length(); ++i) {
+      shiftBy = (shiftBy + diff[i]) % 26;
+      if (shiftBy < 0) {
+        shiftBy += 26;
+      }
+
+      var shifted = (char) ('a' + ((s.charAt(i) - 'a' + shiftBy) % 26));
+      result.setCharAt(i, shifted);
+    }
+
+    return result.toString();
+  }
+}