O(n) time and O(1) space

Author: 149ps

2. Add Two Numbers/2. Add Two Numbers.py

@@ -0,0 +1,36 @@
+"""
+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 contain a single digit. Add the two numbers and return it as a linked list.
+
+You may assume the two numbers do not contain any leading zero, except the number 0 itself.
+
+Example:
+
+Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
+Output: 7 -> 0 -> 8
+Explanation: 342 + 465 = 807.
+"""
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+class Solution:
+    def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode:
+        head1,head2 = l1,l2
+        temp = ListNode(-100)
+        cur = temp
+        carry,total = 0,0
+        while head1 or head2:
+            a = head1.val if head1 else 0
+            b = head2.val if head2 else 0
+            cur_total = a + b + carry
+            carry = cur_total // 10
+            temp.next = ListNode(cur_total % 10)
+            temp = temp.next
+            if head1:
+                head1 = head1.next
+            if head2:
+                head2  = head2.next
+        if carry:
+            temp.next = ListNode(carry)
+        return cur.next