leetcode/cpp/0002.cpp at master · xfmeng17/leetcode · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
  ListNode *addTwoNumbers(ListNode *l1, ListNode *l2) {
    // return func1(l1, l2, 0);
    return func2(l1, l2);
  }

  // ** straight forward recursive solution
  ListNode *func1(ListNode *l1, ListNode *l2, int carry) {
    ListNode *node = new ListNode(0);

    if (l1 == NULL && l2 == NULL) {
      if (carry == 0) {
        return NULL;
      } else {
        node->val = carry;
        return node;
      }
    } else if (l1 != NULL && l2 == NULL) {
      node->val = (l1->val + carry) % 10;
      node->next = func1(l1->next, NULL, (l1->val + carry) / 10);
      return node;
    } else if (l1 == NULL && l2 != NULL) {
      node->val = (l2->val + carry) % 10;
      node->next = func1(NULL, l2->next, (l2->val + carry) / 10);
      return node;
    } else {
      node->val = (l1->val + l2->val + carry) % 10;
      node->next = func1(l1->next, l2->next, (l1->val + l2->val + carry) / 10);
      return node;
    }
  }

  // ** non-recursion solution
  ListNode *func2(ListNode *l1, ListNode *l2) {
    ListNode *head = NULL;
    ListNode *curr = NULL;
    int carry = 0;

    while (l1 || l2 || carry > 0) {
      int val = carry;
      if (l1) {
        val += l1->val;
        l1 = l1->next;
      }
      if (l2) {
        val += l2->val;
        l2 = l2->next;
      }
      carry = val / 10;

      if (curr == NULL) {
        curr = new ListNode(val % 10);
        head = curr;
      } else {
        curr->next = new ListNode(val % 10);
        curr = curr->next;
      }
    }

    return head;
  }
};