1 """ 2 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. 3 You may assume the two numbers do not contain any leading zero, except the number 0 itself. 4 Example: 5 Input: (2 -> 4 -> 3) + (5 -> 6 -> 4) 6 Output: 7 -> 0 -> 8 7 Explanation: 342 + 465 = 807. 8 """ 9 10 """ 11 对于双链表合并的问题，一般方法 12 先建立一个头结点，最后用来返回结果first.next 13 再将头结点复制出一个指针p = first，用来向后增加链表结点 14 对两个链表先同时遍历 while l1 and l2: p=p.next 15 然后再分别单独遍历剩余的 while l1: while l2: 16 """ 17 class ListNode: 18 def __init__(self, x): 19 self.val = x 20 self.next = None 21 22 class Solution1: 23 def addTwoNumbers(self, l1, l2): 24 head = ListNode(0) 25 first = head 26 temp = 0 27 while l1 and l2: 28 if l1.val + l2.val + temp < 10: 29 head.next = ListNode(l1.val+l2.val+temp) 30 temp = 0 31 else: 32 head.next = ListNode((l1.val+l2.val+temp)%10) 33 temp = 1 34 l1 = l1.next 35 l2 = l2.next 36 head = head.next 37 while l1: 38 if l1.val + temp < 10: 39 head.next = ListNode(l1.val+temp) 40 temp = 0 41 else: 42 head.next = ListNode((l1.val+temp)%10) 43 temp = 1 44 l1 = l1.next 45 head = head.next 46 while l2: 47 if l2.val + temp < 10: 48 head.next = ListNode(l2.val+temp) 49 temp = 0 50 else: 51 head.next = ListNode((l2.val+temp)%10) 52 temp = 1 53 l2 = l2.next 54 head = head.next 55 #案例没有通过，加上了下面两行 56 #Input: [5] 57 # [5] 58 #Output: [0] 59 #Expected: [0,1] 60 if temp > 0: 61 head.next = ListNode(1) 62 return first.next 63 64 """ 65 解法二：将三个while循环合并为一个 66 """ 67 class ListNode: 68 def __init__(self, x): 69 self.val = x 70 self.next = None 71 72 class Solution2: 73 def addTwoNumbers(self, l1, l2): 74 first = ListNode(0) 75 p = first 76 carry = 0 77 while l1 or l2: 78 x = l1.val if l1 else 0 #!!!合并while循环的关键的点 79 y = l2.val if l2 else 0 80 res = x + y + carry 81 carry = res // 10 82 p.next = ListNode(res%10) 83 l1 = l1.next if l1 else 0 #!!!合并while循环的关键的点 84 l2 = l2.next if l2 else 0 85 p = p.next 86 if carry > 0: #很容易忽略的情况,最后还有进位 87 p.next = ListNode(1) 88 return first.next