可以使用辅助栈先将其入栈，再反相相加建立链表
该链表建立时应当反向。
/** * 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) { ListNode * head = nullptr; ListNode *p = l1, *q = l2, *tmp = head; stack<int> s1, s2; while(p) { s1.push(p->val); p = p->next; } while(q) { s2.push(q->val); q = q->next; } int carry = 0; while(!s1.empty() || !s2.empty()) { int a = (s1.empty()) ? 0 : s1.top(); int b = (s2.empty()) ? 0 : s2.top(); int sum = a + b + carry; carry = sum / 10; ListNode *tmp = new ListNode(sum % 10); tmp->next = head; head = tmp; if(!s1.empty()) s1.pop(); if(!s2.empty()) s2.pop(); } if(carry) { ListNode *tmp = new ListNode(carry); tmp->next = head; head = tmp; } return head; } };
