merge-two-sorted-lists

gistfile1.txt

https://oj.leetcode.com/problems/merge-two-sorted-lists/

/*
단순히 two runner를 이용해서 merge sort의 merge와 마찬가지로 O(n)에 sorted list를 merge 하는 알고리즘
한번에 accepted 했어야했는데.. linked list pointing 헷갈려서 2번 실패. 아직 pointer 부분 부족한듯
*/

/**
 * 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 == NULL && l2 == NULL) {
            return NULL;
        } else if(l1 == NULL) {
            return l2;
        } else if(l2 == NULL) {
            return l1;
        }
        
        ListNode * head = new ListNode(0);
        ListNode * cur = head;
          
        while(l1 != NULL && l2 != NULL) {
            if(l1->val > l2->val) {
                 cur->next = l2;
                 l2 = l2->next;
            } else {
                cur->next = l1;
                l1 = l1->next;
            }
            
            cur = cur->next;
        }
        
        if(l1 == NULL) {
            cur->next = l2;
        } else if(l2 == NULL) {
            cur->next = l1;
        }
        
        return head->next;
    }
};