Modified code with issues

Author: gunn333

Java/data_structures/linked_lists/Multiply_TwoNums_LL.java

@@ -1,3 +1,28 @@
+/**
+ * MultiplyTwoNumbersLL
+ *
+ * Description:
+ * This class multiplies two numbers represented as singly linked lists.
+ * Each node contains a single digit, and digits are stored in forward order.
+ * The algorithm works by reversing the lists, multiplying digit by digit,
+ * shifting partial results according to place value, adding them together,
+ * and finally reversing the result to get the correct order.
+ *
+ * Use Cases:
+ * - Multiplying very large numbers that cannot fit into primitive data types
+ * - Working with numbers stored in linked list format in memory-efficient
+ * applications
+ *
+ * Time Complexity: O(m * n)
+ * - m = number of nodes in l1
+ * - n = number of nodes in l2
+ * - Each digit of l2 is multiplied with all digits of l1, and partial sums are
+ * added
+ *
+ * Space Complexity: O(m + n)
+ * - For storing the result linked list and intermediate partial products
+ */
+
 class ListNode {
   int data;
   ListNode next;
@@ -8,32 +33,39 @@ class ListNode {
   }
 }
 
-public class MultiplyTwoNumbersLL {
+public class Multiply_TwoNumbers_LL {
 
-  // Multiply two numbers represented as linked lists
+  /**
+   * Multiplies two numbers represented as linked lists
+   */
   public ListNode multiplyTwoNumbers(ListNode l1, ListNode l2) {
     if (l1 == null || l2 == null)
       return new ListNode(0);
 
-    l1 = reverseList(l1);
+    l1 = reverseList(l1); // Reverse to start from least significant digit
     l2 = reverseList(l2);
 
     ListNode result = new ListNode(0);
     ListNode l2Ptr = l2;
     int l2Pos = 0;
 
     while (l2Ptr != null) {
+      // Multiply l1 with current digit of l2
       ListNode partialProduct = multiplyWithSingleDigit(l1, l2Ptr.data);
+
+      // Add zeros to shift the partial product
       partialProduct = addZeros(partialProduct, l2Pos);
+
+      // Add partial product to cumulative result
       result = addTwoNumbers(result, partialProduct);
+
       l2Ptr = l2Ptr.next;
       l2Pos++;
     }
 
-    return reverseList(result.next);
+    return reverseList(result.next); // Reverse final result to correct order
   }
 
-  // Multiply a linked list with a single digit
   private ListNode multiplyWithSingleDigit(ListNode l, int digit) {
     ListNode dummy = new ListNode(0);
     ListNode current = dummy;
@@ -51,7 +83,6 @@ private ListNode multiplyWithSingleDigit(ListNode l, int digit) {
     return dummy.next;
   }
 
-  // Add leading zeros for place value shift
   private ListNode addZeros(ListNode l, int count) {
     while (count-- > 0) {
       ListNode newNode = new ListNode(0);
@@ -61,7 +92,6 @@ private ListNode addZeros(ListNode l, int count) {
     return l;
   }
 
-  // Add two linked list numbers
   private ListNode addTwoNumbers(ListNode l1, ListNode l2) {
     ListNode dummy = new ListNode(0);
     ListNode current = dummy;
@@ -77,10 +107,10 @@ private ListNode addTwoNumbers(ListNode l1, ListNode l2) {
       if (l2 != null)
         l2 = l2.next;
     }
+
     return dummy.next;
   }
 
-  // Reverse a linked list
   private ListNode reverseList(ListNode head) {
     ListNode prev = null, current = head;
     while (current != null) {
@@ -92,7 +122,6 @@ private ListNode reverseList(ListNode head) {
     return prev;
   }
 
-  // Helper function to print linked list
   public static void printList(ListNode head) {
     while (head != null) {
       System.out.print(head.data);
@@ -101,14 +130,12 @@ public static void printList(ListNode head) {
     System.out.println();
   }
 
-  // Example usage
   public static void main(String[] args) {
-    // Number 342
+    // Test case 1: 342 * 465 = 159030
     ListNode l1 = new ListNode(3);
     l1.next = new ListNode(4);
     l1.next.next = new ListNode(2);
 
-    // Number 465
     ListNode l2 = new ListNode(4);
     l2.next = new ListNode(6);
     l2.next.next = new ListNode(5);
@@ -117,6 +144,6 @@ public static void main(String[] args) {
     ListNode result = mt.multiplyTwoNumbers(l1, l2);
 
     System.out.print("Product: ");
-    printList(result); // Expected output: 159030
+    printList(result);
   }
 }