Getting dish dog leetcode | 21. merge two ordered lists

Merge two ordered lists

Title Description

The two ordered lists into a new sorted list and return. The new list is by all nodes in a given mosaic composed of two lists.

Example:

输入：1->2->4, 1->3->4
输出：1->1->2->3->4->4

Problem-solving ideas

Recursive solution is universal, the main idea is to have recursion. Linked lists, binary trees are relatively large probability using recursive 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(l2 == NULL){
            return l1;
        }
        if(l1 == NULL && l2 != NULL){
            return l2;
        }
        if(l1->val < l2->val){
            l1->next = mergeTwoLists(l1->next, l2);
            return l1;
        }
        else{
            l2->next = mergeTwoLists(l2->next, l1);
            return l2;
        }
    }
};