[leetcode 21] Merge Two Sorted Lists

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

오름차순순으로 리스트를 합치자.

 

Example 1:

Input: l1 = [1,2,4], l2 = [1,3,4] Output: [1,1,2,3,4,4]

Example 2:

Input: l1 = [], l2 = [] Output: []

Example 3:

Input: l1 = [], l2 = [0] Output: [0]

 

풀이:

-포인터만 잘 활용한다면 쉬운 문제이다.

- 난이도: easy

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    
    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
        
        ListNode *result = new ListNode(0);
        ListNode *cur = result;
        
        while(l1!=nullptr || l2!=nullptr){
            
            if(l1 == nullptr){
                cur->next = l2;
                break;
            }
            
            if(l2 == nullptr){
                cur->next = l1;
                break;
            }
            
            if(l1 -> val < l2 ->val){
                cur -> next = l1;
                l1 = l1->next;
            }else {
                cur -> next = l2;
                l2 = l2->next;
            }
            cur = cur->next;
        }
        
        return result -> next;
    }
};