主要注意别手误，每个if else情况写全。
1 /** 2 * Definition for singly-linked list. 3 * struct ListNode { 4 * int val; 5 * ListNode *next; 6 * ListNode(int x) : val(x), next(NULL) {} 7 * }; 8 */ 9 class Solution { 10 public: 11 ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) { 12 ListNode *ret = new ListNode(0); 13 ListNode *tl, *node = ret; 14 int tt = 0; 15 while(true){ 16 if(l1){ 17 if(l2){ 18 int tmp = l1->val+l2->val+tt; 19 if(tmp>=10) { 20 node->val = tmp-10; 21 tt = 1; 22 }else{ 23 node->val = tmp; 24 tt = 0; 25 } 26 l1 = l1->next; 27 l2 = l2->next; 28 node->next = new ListNode(0); 29 tl = node; 30 node = node->next; 31 }else{ 32 while(l1){ 33 int tmp = l1->val+tt; 34 if(tmp>=10) { 35 node->val = tmp-10; 36 tt = 1; 37 }else{ 38 node->val = tmp; 39 tt = 0; 40 } 41 l1 = l1->next; 42 node->next = new ListNode(0); 43 tl = node; 44 node = node->next; 45 } 46 break; 47 } 48 }else if(l2){ 49 while(l2){ 50 int tmp = l2->val+tt; 51 if(tmp>=10) { 52 node->val = tmp-10; 53 tt = 1; 54 }else{ 55 node->val = tmp; 56 tt = 0; 57 } 58 l2 = l2->next; 59 node->next = new ListNode(0); 60 tl = node; 61 node = node->next; 62 } 63 break; 64 }else{ 65 break; 66 } 67 } 68 69 if(tt){ 70 node->val = 1; 71 }else{ 72 delete node; 73 tl->next = NULL; 74 } 75 76 return ret; 77 } 78 };