LeetCode Q21: Merge two sorted lists

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.

The easiest way is to use recursion.

	/**
	* 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* p=NULL;
	if(l1==NULL)
	return l2;
	if(l2==NULL)
	return l1;
	if(l1->val<l2->val){
	p=l1;
	l1=l1->next;
	p->next=mergeTwoLists(l1, l2);
	}else{
	p=l2;
	l2=l2->next;
	p->next=mergeTwoLists(l1, l2);
	}
	return p;
	}
	};

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