Merge remote-tracking branch 'origin/GoldbachBranch1' into GoldbachBranch1

Author: BILLSARAN

src/main/java/com/thealgorithms/strings/Upper.java

@@ -21,15 +21,19 @@ public static void main(String[] args) {
      * @return the {@code String}, converted to uppercase.
      */
     public static String toUpperCase(String s) {
-        if (s == null || s.isEmpty()) {
+        if (s == null) {
+            throw new IllegalArgumentException("Input string connot be null");
+        }
+        if (s.isEmpty()) {
             return s;
         }
-        char[] values = s.toCharArray();
-        for (int i = 0; i < values.length; ++i) {
-            if (Character.isLetter(values[i]) && Character.isLowerCase(values[i])) {
-                values[i] = Character.toUpperCase(values[i]);
+        StringBuilder result = new StringBuilder(s);
+        for (int i = 0; i < result.length(); ++i) {
+            char currentChar = result.charAt(i);
+            if (Character.isLetter(currentChar) && Character.isLowerCase(currentChar)) {
+                result.setCharAt(i, Character.toUpperCase(currentChar));
             }
         }
-        return new String(values);
+        return result.toString();
     }
 }

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

@@ -1,41 +1,38 @@
 package com.thealgorithms.strings.zigZagPattern;
 
 final class ZigZagPattern {
+
     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 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;
         }
-        int start = 0;
-        int index = 0;
-        int height = 1;
-        int depth = numRows;
-        char[] zigZagedArray = new char[s.length()];
-        while (depth != 0) {
-            int pointer = start;
-            int heightSpace = 2 + ((height - 2) * 2);
-            int depthSpace = 2 + ((depth - 2) * 2);
-            boolean bool = true;
-            while (pointer < s.length()) {
-                zigZagedArray[index++] = s.charAt(pointer);
-                if (heightSpace == 0) {
-                    pointer += depthSpace;
-                } else if (depthSpace == 0) {
-                    pointer += heightSpace;
-                } else if (bool) {
-                    pointer += depthSpace;
-                    bool = false;
-                } else {
-                    pointer += heightSpace;
-                    bool = true;
+
+        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.append(s.charAt(j));
+
+                if (row > 0 && row < numRows - 1) {
+                    int diagonal = j + cycleLength - 2 * row;
+                    if (diagonal < s.length()) {
+                        result.append(s.charAt(diagonal));
+                    }
                 }
             }
-            height++;
-            depth--;
-            start++;
         }
-        return new String(zigZagedArray);
+
+        return result.toString();
     }
 }

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

@@ -6,10 +6,14 @@
 public class ZigZagPatternTest {
 
     @Test
-    public void palindrome() {
+    public void testZigZagPattern() {
         String input1 = "HelloWorldFromJava";
         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
     }
 }