题解 | #两个链表生成相加链表#

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */

class Solution {
public:
    /**
     * 
     * @param head1 ListNode类 
     * @param head2 ListNode类 
     * @return ListNode类
     */
    ListNode* reverseList(ListNode* head){
        if(head==nullptr) return nullptr;
        ListNode* cur=head;
        ListNode* node=nullptr;
        ListNode* next;
        while(cur!=nullptr){
            next = cur->next;
            cur->next=node;
            node = cur;
            cur=next;
        }
        return node;
    }


    ListNode* addInList(ListNode* head1, ListNode* head2) {
        // write code here
        if(head1==nullptr){ return head2;}
        if(head2==nullptr){ return head1;}
        head1 = reverseList(head1);
        head2 = reverseList(head2);
        int num;
        int jinwei=0;
        ListNode* resNode=new ListNode(-1);
        ListNode* resHead=resNode;
        while(head1!=nullptr&&head2!=nullptr){
            num = head1->val + head2->val +jinwei;
            jinwei=0;
            if(num>9){ jinwei = 1; num=num-10;}
            ListNode* node = new ListNode(num);
            resNode->next = node;
            resNode = node;
            head1=head1->next;
            head2=head2->next;
        }

        if(head1==nullptr){
            while(head2!=nullptr){
                num = head2->val + jinwei;
                jinwei=0;
                if(num>9){ jinwei=1;num=num-10;}
                ListNode* node = new ListNode(num);
                resNode->next = node;
                resNode = node;
                head2=head2->next;
            }
            if(jinwei!=0){
                ListNode* node = new ListNode(jinwei);
                jinwei=0;
                resNode->next = node;
                resNode = node;
                resNode->next=nullptr;
            }
            resHead->next = reverseList(resHead->next);
            return resHead->next;
        }

         if(head2==nullptr){
            while(head1!=nullptr){
                num = head1->val + jinwei;
                jinwei=0;
                if(num>9){ jinwei=1;num=num-10;}
                ListNode* node = new ListNode(num);
                resNode->next = node;
                resNode = node;
                head1=head1->next;
            }
            if(jinwei!=0){
                ListNode* node = new ListNode(jinwei);
                jinwei=0;
                resNode->next = node;
                resNode = node;
                resNode->next=nullptr;
            }
             resHead->next = reverseList(resHead->next);
             return resHead->next;
        }

        return nullptr;
    }
};