Docs: add Javadoc to CoinChange class and method (#7424)

* Fix: remove floating Javadoc comments causing compilation error

* Docs: add Javadoc to CoinChange class and method

* Style: apply clang-format to CoinChange.java

Author: BixbyCodes

src/main/java/com/thealgorithms/greedyalgorithms/CoinChange.java

@@ -6,10 +6,30 @@
 
 // Problem Link : https://en.wikipedia.org/wiki/Change-making_problem
 
+/**
+ * The Coin Change problem finds the minimum number of coins needed
+ * to make a given amount using a greedy approach.
+ *
+ * <p>Note: This greedy approach works optimally for standard coin systems
+ * (like Indian currency), but may not work for all arbitrary coin sets.
+ * For arbitrary denominations, dynamic programming is preferred.
+ *
+ * @see <a href="https://en.wikipedia.org/wiki/Change-making_problem">Change-making problem</a>
+ */
 public final class CoinChange {
     private CoinChange() {
     }
-    // Function to solve the coin change problem
+
+    /**
+     * Returns the list of coins used to make the given amount
+     * using a greedy algorithm with standard denominations.
+     *
+     * <p>Time Complexity: O(n log n) where n is the number of coin denominations
+     * <p>Space Complexity: O(n)
+     *
+     * @param amount the total amount to make change for
+     * @return list of coins used to make the amount
+     */
     public static ArrayList<Integer> coinChangeProblem(int amount) {
         // Define an array of coin denominations in descending order
         Integer[] coins = {1, 2, 5, 10, 20, 50, 100, 500, 2000};