Add the two numbers of linked list given in reverse order and return the sum as a linked list in reverse order

Author: Antesh Sharma

src/main/java/com/antesh/dsa/linkedlist/AddTwoNumbersLinkedList.java

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+package com.antesh.dsa.linkedlist;
+/**
+ * Problem Reference: https://github.com/aniketskulkarni/coding-problems/blob/master/LeetCode/src/com/java7/problem/easy/linkedlist/AddTwoNumbersLinkedList.java
+ * You are given two non-empty linked lists representing two non-negative
+ * integers. The digits are stored in reverse order, and each of their nodes
+ * contains a single digit. Add the two numbers and return the sum as a linked
+ * list.
+ * You may assume the two numbers do not contain any leading zero, except the
+ * number 0 itself.
+ *
+ * Input: l1 = [2,4,3], l2 = [5,6,4]
+ * Output: [7,0,8]
+ * Explanation: 342 + 465 = 807.
+ *
+ * Input: l1 = [0], l2 = [0]
+ * Output: [0]
+ *
+ * Input: l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]
+ * Output: [8,9,9,9,0,0,0,1]
+ */
+public class AddTwoNumbersLinkedList {
+
+    Node n1;
+    Node n2;
+    Node result;
+
+    class Node {
+        int data;
+        Node next;
+
+        public Node(int data) {
+            this.data = data;
+            this.next = null;
+        }
+    }
+
+    public String print(Node n) {
+        StringBuilder sb = new StringBuilder();
+        while (n1 != null) {
+            sb.append(n1.data).append(" --> ");
+        }
+        return sb.toString();
+    }
+
+    public Node addToTail(Node head, int data) {
+        if (head == null) {
+            head = new Node(data);
+            return head;
+        }
+
+        Node ptr = head;
+        while (ptr.next != null) {
+            ptr = ptr.next;
+        }
+        ptr.next = new Node(data);
+
+        return head;
+    }
+
+    public Node addTwoNumbers(Node n1, Node n2) {
+        if (n1 == null && n2 == null) return null;
+        if (n1 == null) return n2;
+        if (n2 == null) return n1;
+
+        Node result = null;
+        int carry = 0;
+
+        while (n1 != null && n2 != null) {
+            int sum = carry + n1.data + n2.data;
+            if ( sum > 9) {
+                carry = 1;
+                sum = sum % 10;
+            }
+
+            result = addToTail(result, sum);
+
+            n1 = n1.next;
+            n2 = n2.next;
+        }
+
+        while (n1 != null) {
+            addToTail(result, n1.data + carry);
+            carry = 0;
+            n1 = n1.next;
+        }
+
+        while (n2 != null) {
+            addToTail(result, n2.data + carry);
+            carry = 0;
+            n2 = n2.next;
+        }
+
+        if (carry > 0) {
+            result = addToTail(result, carry);
+        }
+
+        return result;
+    }
+
+    public static void main(String[] args) {
+        AddTwoNumbersLinkedList list = new AddTwoNumbersLinkedList();
+        for (int i = 3; i < 6; i++) {
+            list.n1 = list.addToTail(list.n1, i);
+            list.n2 = list.addToTail(list.n2, i);
+        }
+
+        list.addTwoNumbers(list.n1, list.n2);
+    }
+}