[LeetCode] Add Two Numbers(stored in List)

首先，演示一个错误的reverList

class Solution {
    public:
        ListNode* reverse(ListNode* root)
        {
            if(NULL == root)
                return NULL;
            ListNode* pCur = root;
            ListNode* pNext = root->next;

            while(pNext)
            {
                pNext = pNext->next;
                pCur->next->next = pCur;
                pCur = pCur->next;
            }
            root->next = NULL;
            return pCur;
        }

};

(2)--------->(3)-------->(4)----------->(5)--------->NULL

首先pCur指向2,pNext指向3；

pNext=pNext->next; pNext指向4，

pCur->next->next = pCur，然后3--->4 的指针断了， 从此pCur就自己转圈了。。。

正确的reverseList

ListNode * reverseList(ListNode* head)
{
    if(head == NULL) return NULL;

    ListNode *pre = NULL;
    ListNode *cur = head;
    ListNode *next = NULL;

    while(cur)
    {
        next = cur->next;
        cur->next = pre;

        pre = cur;
        cur = next;
    }

    return pre;

}

这个题目也不难，注意dummy节点的使用，另外，记得最后carrybit的处理

/**
 * 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)
        {
            if(l1 == NULL)
                return l2;
            if(l2 == NULL)
                return l1;

            ListNode* p1 = l1;
            ListNode* p2 = l2;
            ListNode dummy(-1);
            ListNode* pNew = &dummy;
            int carry = 0;
            int sum = 0;

            while(p1 && p2)
            {
                sum = (p1->val + p2->val + carry)%10;
                carry= (p1->val + p2->val + carry)/10;
                pNew->next = new ListNode(sum);
                pNew = pNew->next;
                p1 = p1->next;
                p2 = p2->next;
            }

            while(p1)
            {
                sum = (p1->val +  carry)%10;
                carry= (p1->val + carry)/10;
                pNew->next = new ListNode(sum);
                pNew = pNew->next;
                p1 = p1->next;
            }

            while(p2)
            {
                sum = (p2->val +  carry)%10;
                carry= (p2->val + carry)/10;
                pNew->next = new ListNode(sum);
                pNew = pNew->next;
                p2 = p2->next;
            }

            if(carry)
            {
                pNew->next = new ListNode(carry);
                pNew = pNew->next;
            } 
            
            return dummy.next;
        }
              
};