reduce mutable state

Author: r4lly99

src/main/java/com/thealgorithms/strings/zigZagPattern/ZigZagPattern.java

@@ -9,31 +9,30 @@ private ZigZagPattern() {
      * Encodes a given string into a zig-zag pattern.
      *
      * @param s       the input string to be encoded
-     * @param numRows the number of rows in the zig-zag pattern
-     * @return the encoded string in zig-zag pattern format
+     * @param numRows the number of rows in the zigzag pattern
+     * @return the encoded string in zigzag pattern format
      */
     public static String encode(String s, int numRows) {
         if (numRows < 2 || s.length() < numRows) {
             return s;
         }
 
-        char[] result = new char[s.length()];
-        int index = 0;
-
-        // Cycle length for zigzag traversal
+        StringBuilder result = new StringBuilder(s.length());
         int cycleLength = 2 * numRows - 2;
 
         for (int row = 0; row < numRows; row++) {
             for (int j = row; j < s.length(); j += cycleLength) {
-                result[index++] = s.charAt(j);
+                result.append(s.charAt(j));
 
-                int diagonal = j + cycleLength - 2 * row;
-                if (row > 0 && row < numRows - 1 && diagonal < s.length()) {
-                    result[index++] = s.charAt(diagonal);
+                if (row > 0 && row < numRows - 1) {
+                    int diagonal = j + cycleLength - 2 * row;
+                    if (diagonal < s.length()) {
+                        result.append(s.charAt(diagonal));
+                    }
                 }
             }
         }
 
-        return new String(result);
+        return result.toString();
     }
 }

src/test/java/com/thealgorithms/strings/zigZagPattern/ZigZagPatternTest.java

@@ -11,5 +11,9 @@ public void testZigZagPattern() {
         String input2 = "javaIsAProgrammingLanguage";
         Assertions.assertEquals(ZigZagPattern.encode(input1, 4), "HooeWrrmalolFJvlda");
         Assertions.assertEquals(ZigZagPattern.encode(input2, 4), "jAaLgasPrmgaaevIrgmnnuaoig");
+        // Edge cases
+        Assertions.assertEquals("ABC", ZigZagPattern.encode("ABC", 1)); // Single row
+        Assertions.assertEquals("A", ZigZagPattern.encode("A", 2)); // numRows > length of string
+        Assertions.assertEquals("", ZigZagPattern.encode("", 3)); // Empty string
     }
 }