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.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)

Output: 7 -> 0 -> 8

 

现在做题不仅要ac，还要找到比较高效的做法。这道题目是两个链表相加，很容易想到边界条件，不过我开始的代码写的有些臃肿，而且变量名也很中式。代码如下：

class ListNode(object):     def __init__(self, x):         self.val = x         self.next = Noneclass Solution(object):    def addTwoNumbers(self, l1, l2):        """        :type l1: ListNode        :type l2: ListNode        :rtype: ListNode        """        p = ListNode(0)        ans = p        jinwei = 0        while l1 and l2:            jieguo = (l1.val + l2.val + jinwei) % 10            jinwei = (l1.val + l2.val + jinwei) / 10            p.val = jieguo            l1 = l1.next            l2 = l2.next            if l1 and l2:                p.next = ListNode(0)                p = p.next        if l1 and not l2:            while l1:                jieguo = (l1.val + jinwei) % 10                jinwei = (l1.val + jinwei) / 10                p.next = ListNode(jieguo)                p = p.next                l1 = l1.next        if l2 and not l1:            while l2:                jieguo = (l2.val + jinwei) % 10                jinwei = (l2.val + jinwei) / 10                p.next = ListNode(jieguo)                p = p.next                l2 = l2.next        if jinwei > 0:            p.next = ListNode(0)            p.next.val = jinwei        return ansif __name__ == '__main__':    n0 = ListNode(2)    n1 = ListNode(4)    n2 = ListNode(3)    n3 = ListNode(5)    n4 = ListNode(6)    n5 = ListNode(4)    n0.next = n1    n1.next = n2    n3.next = n4    n4.next = n5    s = Solution()     ans = s.addTwoNumbers(n0, n3)    while ans:        print ans.val        ans = ans.next

可以看到有很多重复的代码，运行起来并不高效。

来看下面的代码，进位英文是carry

class ListNode(object):     def __init__(self, x):         self.val = x         self.next = Noneclass Solution(object):    def addTwoNumbers(self, l1, l2):        """        :type l1: ListNode        :type l2: ListNode        :rtype: ListNode        """        pHead = ListNode(0)        cur = pHead        carry = 0        total = 0        while l1 or l2:            x = l1.val if l1 else 0            y = l2.val if l2 else 0            total = x + y + carry            carry = total / 10            cur.next = ListNode(total % 10)            cur = cur.next            if l1:                l1 = l1.next            if l2:                l2 = l2.next        if carry > 0:            cur.next = ListNode(carry)        return pHead.next