Add Two Numbers

You are given two linked lists representing two non-negative numbers. 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.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

 1 /**

 2  * Definition for singly-linked list.

 3  * public class ListNode {

 4  *     int val;

 5  *     ListNode next;

 6  *     ListNode(int x) {

 7  *         val = x;

 8  *         next = null;

 9  *     }

10  * }

11  */

12 public class Solution {

13     public ListNode addTwoNumbers(ListNode l1, ListNode l2) {

14         // Start typing your Java solution below

15         // DO NOT write main() function

16         ListNode answer = null;

17         ListNode next_node = null;

18         ListNode cur_node = null;

19         int carry = 0;

20         int sum   = 0;

21         boolean head = true;

22         ListNode l1_next = l1.next;

23         ListNode l1_cur  = l1;

24         ListNode l2_next = l2.next;

25         ListNode l2_cur  = l2;

26         while(l1_cur != null && l2_cur != null){

27             if((sum = l1_cur.val + l2_cur.val + carry) < 10){

28                 carry = 0;

29                 if(head == true){

30                     cur_node = new ListNode(sum);

31                     answer = cur_node;

32                     head = false;

33                 }

34                 else{

35                     ListNode new_node = new ListNode(sum);

36                     cur_node.next = new_node;

37                     cur_node = new_node;

38                 }

39             }

40             else{

41                 carry = 1;

42                 sum -= 10;

43                 if(head == true){

44                     cur_node = new ListNode(sum);

45                     answer = cur_node;

46                     head = false;

47                 }

48                 else{

49                     ListNode new_node = new ListNode(sum);

50                     cur_node.next = new_node;

51                     cur_node = new_node;

52                 }

53             }

54             l1_cur  = l1_cur.next;

55             l2_cur  = l2_cur.next;

56         }

57 

58         while(l1_cur != null){

59             if((sum = l1_cur.val + carry) < 10){

60                 carry = 0;

61                 ListNode new_node = new ListNode(sum);

62                 cur_node.next = new_node;

63                 cur_node = new_node;

64             }

65             else{

66                 carry = 1;

67                 sum -= 10;

68                 ListNode new_node = new ListNode(sum);

69                 cur_node.next = new_node;

70                 cur_node = new_node;

71             }

72             l1_cur  = l1_cur.next;

73         }

74         while(l2_cur != null){

75             if((sum = l2_cur.val + carry) < 10){

76                 carry = 0;

77                 ListNode new_node = new ListNode(sum);

78                 cur_node.next = new_node;

79                 cur_node = new_node;

80             }

81             else{

82                 carry = 1;

83                 sum -= 10;

84                 ListNode new_node = new ListNode(sum);

85                 cur_node.next = new_node;

86                 cur_node = new_node;

87             }

88             l2_cur  = l2_cur.next;

89         }

90         if(l1_cur == null && l2_cur == null && carry == 1){

91             ListNode new_node = new ListNode(carry);

92             cur_node.next = new_node;

93             cur_node = new_node;

94         }

95         return answer;

96     }

97 }

这一题还是挺简单的，就是有很多test case 需要考虑。。。 下次要争取一次考虑完全

 第二遍：

 1 public class Solution {

 2     public ListNode addTwoNumbers(ListNode l1, ListNode l2) {

 3         // Start typing your Java solution below

 4         // DO NOT write main() function

 5         ListNode header = new ListNode(-1);

 6         ListNode cur = header;

 7         int carry = 0;

 8         while(l1 != null || l2 != null){

 9             if(l1 != null){

10                 carry += l1.val;

11                 l1 = l1.next;

12             }

13             if(l2 != null){

14                 carry += l2.val;

15                 l2 = l2.next;

16             }

17             ListNode tmp = new ListNode(carry % 10);

18             cur.next = tmp;

19             cur = cur.next;

20             carry /= 10;

21         }

22         if(carry != 0){

23             ListNode tmp = new ListNode(carry);

24             cur.next = tmp;

25         }

26         return header.next;

27     }

28 }