Leetcode (*)141 2 (ok)21

141. Linked List Cycle(*)

class Solution {
public:
    bool hasCycle(ListNode *head) {
        ListNode* slow = head;
        ListNode* fast = head;
        while(fast != NULL && fast->next != NULL){
            slow = slow->next;
            fast = fast->next->next;
            if(fast == slow) return true;
        }
        return false;

    }
};

2. Add Two Numbers(*)

class Solution {
public:
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
        ListNode* p1 = l1;
        ListNode* p2 = l2;
        ListNode* dummy = new ListNode(-1);
        ListNode* p = dummy;

        int carry = 0;
        while(p1 != NULL || p2 != NULL || carry > 0){
            int val = carry;
            if(p1 != NULL){
                val += p1->val;
                p1 = p1->next;
            }
            if(p2 != NULL){
                val += p2->val;
                p2 = p2->next;
            }
            carry = val/10;
            val = val%10;
            p->next = new ListNode(val);
            p = p->next;
        }
        return dummy->next;

    }
};

进位

21. Merge Two Sorted Lists（ok）

class Solution {
public:
    ListNode* mergeTwoLists(ListNode* list1, ListNode* list2) {
        ListNode* p1 = list1;
        ListNode* p2 = list2;
        ListNode* dummy = new ListNode(-1);
        ListNode* p = dummy;

        while(p1 != NULL && p2 != NULL){
            if(p1->val <= p2->val){
                p->next = p1;
                p1 = p1->next;
            }else{
                p->next = p2;
                p2 = p2->next;
            }
            p = p->next;
        }

        if(p1 != NULL){
            p->next = p1;
        }
        if(p2 != NULL){
            p->next = p2;
        }

        return dummy->next;
    }