update 2.add_two_numbers.java

Author: marklcrns

2.add_two_numbers.java

@@ -0,0 +1,44 @@
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode() {}
+ *     ListNode(int val) { this.val = val; }
+ *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
+ * }
+ */
+class Solution {
+    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
+        // init new ListNode
+        ListNode dummyRoot = new ListNode(0);
+        ListNode l3 = dummyRoot;
+        // init a carry variable to 0
+        int carry = 0;
+        int sum;
+        int x;
+        int y;
+
+        // loop over the size of the biggest ListNode
+        while (l1 != null || l2 != null) {
+            x = (l1 != null) ? l1.val : 0;
+            y = (l2 != null) ? l2.val : 0;
+            // Add l1 and l2 + carry at given index,
+            // storing the 10s place into carry var and the sum into new ListNode
+            sum = x + y + carry;
+            l3.next = new ListNode(sum % 10);
+            // Traverse next node
+            if (l1 != null) l1 = l1.next;
+            if (l2 != null) l2 = l2.next;
+            l3 = l3.next;
+
+            // store carry
+            carry = sum / 10;
+        }
+        // Store carry into last node if > 0
+        if (carry > 0) {
+            l3.next = new ListNode(carry);
+        }
+        return dummyRoot.next;
+    }
+}