Added LinkedList Code in Java

Author: gunn333

Java/data_structures/linked_lists/Multiply_TwoNums_LL.java

@@ -0,0 +1,122 @@
+class ListNode {
+  int data;
+  ListNode next;
+
+  ListNode(int data) {
+    this.data = data;
+    this.next = null;
+  }
+}
+
+public class MultiplyTwoNumbersLL {
+
+  // Multiply 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);
+    l2 = reverseList(l2);
+
+    ListNode result = new ListNode(0);
+    ListNode l2Ptr = l2;
+    int l2Pos = 0;
+
+    while (l2Ptr != null) {
+      ListNode partialProduct = multiplyWithSingleDigit(l1, l2Ptr.data);
+      partialProduct = addZeros(partialProduct, l2Pos);
+      result = addTwoNumbers(result, partialProduct);
+      l2Ptr = l2Ptr.next;
+      l2Pos++;
+    }
+
+    return reverseList(result.next);
+  }
+
+  // Multiply a linked list with a single digit
+  private ListNode multiplyWithSingleDigit(ListNode l, int digit) {
+    ListNode dummy = new ListNode(0);
+    ListNode current = dummy;
+    int carry = 0;
+
+    while (l != null || carry != 0) {
+      int sum = carry + (l != null ? l.data * digit : 0);
+      carry = sum / 10;
+      current.next = new ListNode(sum % 10);
+      current = current.next;
+      if (l != null)
+        l = l.next;
+    }
+
+    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);
+      newNode.next = l;
+      l = newNode;
+    }
+    return l;
+  }
+
+  // Add two linked list numbers
+  private ListNode addTwoNumbers(ListNode l1, ListNode l2) {
+    ListNode dummy = new ListNode(0);
+    ListNode current = dummy;
+    int carry = 0;
+
+    while (l1 != null || l2 != null || carry != 0) {
+      int sum = carry + (l1 != null ? l1.data : 0) + (l2 != null ? l2.data : 0);
+      carry = sum / 10;
+      current.next = new ListNode(sum % 10);
+      current = current.next;
+      if (l1 != null)
+        l1 = l1.next;
+      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) {
+      ListNode next = current.next;
+      current.next = prev;
+      prev = current;
+      current = next;
+    }
+    return prev;
+  }
+
+  // Helper function to print linked list
+  public static void printList(ListNode head) {
+    while (head != null) {
+      System.out.print(head.data);
+      head = head.next;
+    }
+    System.out.println();
+  }
+
+  // Example usage
+  public static void main(String[] args) {
+    // Number 342
+    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);
+
+    MultiplyTwoNumbersLL mt = new MultiplyTwoNumbersLL();
+    ListNode result = mt.multiplyTwoNumbers(l1, l2);
+
+    System.out.print("Product: ");
+    printList(result); // Expected output: 159030
+  }
+}