LeetCode:Merge Two Sorted Lists

Merge Two Sorted Lists

Total Accepted: 128244  Total Submissions: 359937  Difficulty: Easy

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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c++ 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) return l2;
        if(!l2) return l1;
        ListNode *head;
        if(l1->val < l2->val){
            head = l1;
            l1=l1->next;
        }else{
            head = l2;
            l2=l2->next;
        }
        ListNode *phead = head;
        while(l1 && l2) {
            if(l1->val < l2->val) {
                phead->next = l1;
                l1=l1->next;
            }else{
                phead->next = l2;
                l2=l2->next;
            }
            phead=phead->next;
        }
        if(l1) phead->next=l1;
        else phead->next=l2;
        return head;
    }
};