Merge Two Sorted Lists

Question: Merge Two Sorted Lists

Description: Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

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Example:

• Input: 1->2->4, 1->3->4
• Output: 1->1->2->3->4->4

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Solution：

 

 采用两个指针指向两个链表，比较指针对应节点的大小，较小的节点即为下一个节点，同时指针指向下一个节点；

Solution Code：

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2){
        if(l1 == nullptr)
            return l2;
        else if(l2 == nullptr)
            return l1;
        // 两个链表都不为空
        ListNode *pMerge = nullptr;
        if(l1->val < l2->val){
            pMerge = l1;
            pMerge->next = mergeTwoLists(l1->next, l2);
        }
        else{
            pMerge = l2;
            pMerge->next = mergeTwoLists(l1, l2->next);
        }
        return pMerge;
    }
};

Reports: Runtime: 8 ms, faster than 89.04% of C++ online submissions for Merge Two Sorted Lists.