LintCode-165.合并两个排序链表

合并两个排序链表

将两个排序链表合并为一个新的排序链表

样例

给出 1->3->8->11->15->null，2->null， 返回 1->2->3->8->11->15->null。

标签

领英 链表

code

/**
 * Definition of ListNode
 * class ListNode {
 * public:
 *     int val;
 *     ListNode *next;
 *     ListNode(int val) {
 *         this->val = val;
 *         this->next = NULL;
 *     }
 * }
 */
class Solution {
public:
    /**
     * @param ListNode l1 is the head of the linked list
     * @param ListNode l2 is the head of the linked list
     * @return: ListNode head of linked list
     */
    ListNode *mergeTwoLists(ListNode *l1, ListNode *l2) {
        // write your code here
        
        ListNode *pnew,*phead = l1;

        if(l1 == NULL)  {
            return l2;
        }
        else if(l2 == NULL) {
            return l1;
        }
        else {
            if(l1->val <= l2->val) {
                phead = pnew = l1;
                l1 = l1->next;
            }
            else {
                phead = pnew = l2;
                l2 = l2->next;
            }
            while(l1!=NULL && l2!=NULL) {
                if(l1->val <= l2->val) {
                    pnew->next = l1;
                    l1 = l1->next;
                    pnew = pnew->next;
                }
                else {
                    pnew->next = l2;
                    l2 = l2->next;
                    pnew = pnew->next;
                }
            }
            if(l1!=NULL && l2==NULL) {
                pnew->next = l1;
            }
            if(l2!=NULL && l1==NULL) {
                pnew->next = l2;
            }
            return phead;
        }
    }
};