21. Merge Two Sorted Lists

21. Merge Two Sorted Lists

 

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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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思路：用一个头结点来引导，当链表A和链表B 都还剩的时候，依次将较小的插到答案链表的尾部，最后将剩余的部分置到末尾

</pre><pre code_snippet_id="1751072" snippet_file_name="blog_20160707_3_8839822" name="code" class="cpp">
 struct ListNode {
      int val;
      ListNode *next;
      ListNode(int x) : val(x), next(NULL) {}
  };
class Solution {
public:
    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
        ListNode *ans=new ListNode(0);
        ListNode *answer=ans;
        while(l1 && l2){
            if(l1->val<l2->val){
                ans->next=l1;
                ans=ans->next;
                l1=l1->next;
            }
            else{
                ans->next=l2;
                l2=l2->next;
                ans=ans->next;
            }
        }
        if(l1){
            ans->next=l1;
        }
        if(l2){
            ans->next=l2;
        }
        
        return answer->next;
    }
};