題目

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.

Example:

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

思路

定義一個頭結點，然後迴圈對l1和l2比較，插入較小的節點，直到兩者有一個到了尾節點。最後把沒有達到尾節點的接到連結串列後即可。

程式碼

/**
 * 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) {

        ListNode node(0);
        ListNode* head = &node;
        ListNode* temp = head; 

        while
 
(l1!=NULL && l2!=NULL){

            if(l1->val<l2->val){
                temp->next = l1;
                l1 = l1->next;
            }else{

                temp->next = l2;
                l2 = l2->next;
            }

            temp = temp->next;
        }

        temp->next
 
 = l1?l1:l2;
        return head->next;
    }
};