docs(strings): add reference URL to MoveHashToEnd Javadoc

Author: ShyamChavda005

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

@@ -0,0 +1,56 @@
+package com.thealgorithms.strings;
+
+/**
+ * Moves all '#' characters to the end of the given string while preserving
+ * the order of the other characters.
+ *
+ * Example:
+ * Input  : "h#e#l#llo"
+ * Output : "hello###"
+ *
+ * The algorithm works by iterating through the string and collecting
+ * all non-# characters first, then filling the remaining positions
+ * with '#'.
+ *
+ * Time Complexity: O(n)
+ * Space Complexity: O(n)
+ *
+ * @see <a href="https://www.geeksforgeeks.org/move-special-char-end-string-maintain-order-alphabets/">Move all special characters to end - GeeksForGeeks</a>
+ */
+public final class MoveHashToEnd {
+
+    /**
+     * Private constructor to prevent instantiation of utility class.
+     */
+    private MoveHashToEnd() {
+    }
+
+    /**
+     * Moves all '#' characters in the input string to the end.
+     *
+     * @param str the input string containing characters and '#'
+     * @return a new string with all '#' characters moved to the end
+     */
+    public static String moveHashToEnd(String str) {
+        if (str == null || str.isEmpty()) {
+            return str;
+        }
+
+        char[] arr = str.toCharArray();
+        int insertPos = 0;
+
+        // Place all non-# characters at the beginning
+        for (char ch : arr) {
+            if (ch != '#') {
+                arr[insertPos++] = ch;
+            }
+        }
+
+        // Fill remaining positions with '#'
+        while (insertPos < arr.length) {
+            arr[insertPos++] = '#';
+        }
+
+        return new String(arr);
+    }
+}