Leetcode: 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.

递归解决很简单

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

/**
 * 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,q,r,head;
        
        if(l1=NULL && l2==NULL)
        {
            return NULL;
        }
        if(l1==NULL)
        {
            return l2;
        }
        if(l2==NULL)
        {
            return l1;
        }
        p=l1;
        q=l2;
        head=NULL;
        if(p.val<=q.val)
        {
            head=p;
            p=p->next;
        }
        else
        {
            head=q;
            q=q->next;
        }
        r=head;
        while(p!NULL && q!=NULL)
        {
            if(p->val<=q.val)
            {
                r->next=p;
                r=p;
                p=p->next;
            }
            else
            {
                r->next=q;
                r=q;
                q=q->next;
            }
        }
        if(p==NULL)
        {
            while(q!=NULL)
            {
                r->next=q;
                r=q;
                q=q->next;
            }
        }
        else
        {
            while(p!=NULL)
            {
                r->next=p;
                r=p;
                p=p->next;
            }
        }
        return head;
        
    }
};

Leetcode: Merge Two Sorted Lists

原文：http://blog.csdn.net/flyljg/article/details/47381237