leetcode 21. Merge Two Sorted Lists

问题描述:

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.

代码如下: 6ms

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
struct ListNode* mergeTwoLists(struct ListNode* l1, struct ListNode* l2) 
{
    if(!l1 && !l2)
        return NULL;
        
    struct ListNode *pList = (struct ListNode *)malloc(sizeof(struct ListNode));
    struct ListNode *pNode = NULL;
    struct ListNode *pHead = pList;
  
    while(l1 && l2)
    {
        pNode = (struct ListNode *)malloc(sizeof(struct ListNode));
        if(l1->val < l2->val)
        {
            pNode->val = l1->val;
            l1 = l1->next;
        }
        else
        {
             pNode->val = l2->val;
             l2 = l2->next;
        }
        pNode->next = NULL;
        pList->next = pNode;
        pList       = pNode;
    }
    
    while(l1)
    {
        pNode = (struct ListNode *)malloc(sizeof(struct ListNode));
        pNode->val  = l1->val;
        pNode->next = NULL;
        pList->next = pNode;
        pList       = pNode;
        l1          = l1->next;
    }
    
    while(l2)
    {
        pNode = (struct ListNode *)malloc(sizeof(struct ListNode));
        pNode->val  = l2->val;
        pNode->next = NULL;
        pList->next = pNode;
        pList       = pNode;
        l2          = l2->next;
    }
    
    return pHead->next;
}