LeetCode 2:《Add Two Numbers》

 编程思路：遍历两个两个链表，获得存储的整数值，进行加法运算，然后将结果存入链表中，返回链表的头。

import math

# Definition for singly-linked list.
class ListNode:
    def __init__(self, x):
        self.val = x
        self.next = None

class Solution:
    # @return a ListNode
    def addTwoNumbers(self, l1, l2):
        # 传入的是两个链表的头
        # 遍历获取各个节点，计算存储的整数值
        num_1, num_2 = 0, 0
        p, q = l1, l2
        i, j = 0, 0
        while p != None:
            num_1 = num_1 + p.val*math.pow(10, i)
            p = p.next
            i = i + 1
        while q != None:
            num_2 = num_2 + q.val*math.pow(10, j)
            q = q.next
            j = j + 1
        num_3 = int(num_1 + num_2)
        # 整数转字符串，便于截取各个位上的数
        num_s = str(num_3)
        # 设置链表头，以及前一个节点
        head = None
        previous = None
        for i in range(len(num_s)):
            value = int(num_s[len(num_s)-i-1:len(num_s)-i])
            node = ListNode(value)
            if i == 0:
                head = node
            else:
                previous.next = node
            previous = node 
        return head