两数相加

# 定义链表
class ListNode:
    def __init__(self, x):
        self.val = x
        self.next = None
class Solution:
    def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode:
        # 这里new出的这个节点仅仅是为了开个头，最后return的时候返回的是prenode.next
        prenode = ListNode(0)
        lastnode = prenode
        # val用于记录进位
        val = 0
        # while中当为0，None的时候终止循环
        while val or l1 or l2:
            # divmod函数返回一个包含商和余数的元组
            val, cur = divmod(val + (l1.val if l1 else 0) + (l2.val if l2 else 0), 10)
            # 把余数作为下一个节点
            lastnode.next = ListNode(cur)
            lastnode = lastnode.next
            # 如果两个都为None了则终止循环
            l1 = l1.next if l1 else None
            l2 = l2.next if l2 else None
        return prenode.next
def generateList(l: list) -> ListNode:
    prenode = ListNode(0)
    lastnode = prenode
    for val in l:
        lastnode.next = ListNode(val)
        lastnode = lastnode.next
    return prenode.next
def printList(l: ListNode):
    while l:
        print("%d, " %(l.val), end = ‘‘)
        l = l.next
    print(‘‘)
if __name__ == "__main__":
    l1 = generateList([1, 5, 8])
    l2 = generateList([9, 1, 2, 9])

    printList(l1)
    printList(l2)
    s = Solution()
    sum = s.addTwoNumbers(l1, l2)
    printList(sum)