合并两个排序的链表.cpp

//输入两个单调递增的链表，输出两个链表合成后的链表，当然我们需要合成后的链表满足单调不减规则。
/*
struct ListNode {
	int val;
	struct ListNode *next;
	ListNode(int x) :
			val(x), next(NULL) {
	}
};*/
class Solution {
public:
    ListNode* Merge(ListNode* pHead1, ListNode* pHead2)
    {
        ListNode *result  = NULL;
        ListNode *current = NULL;

        if(pHead1 == NULL)
            return pHead2;
        if(pHead2 == NULL)
            return pHead1;
            /*
                    if(pHead1->val <= pHead2->val){
                        result = pHead1;
                        result->next = Merge(pHead1->next, pHead2);
                    } else {
                        result = pHead2;
                        result->next = Merge(pHead1, pHead2->next);
                    }
            */
        while(pHead1 != NULL && pHead2 != NULL)
        {
            if(pHead1->val <= pHead2->val)
            {
                if(result == NULL)
                {
                    current = result = pHead1;
                }else
                {
                    current->next = pHead1;
                    current       = current->next;
                }
                pHead1 = pHead1->next;
            }else
            {
                if(result == NULL)
                {
                    current = result = pHead2;
                }else
                {
                    current->next = pHead2;
                    current = current->next;
                }
                pHead2 = pHead2->next;
            }
        }
        if(pHead1 == NULL)
            current->next = pHead2;
        if(pHead2 == NULL)
            current->next = pHead1;
        
        return result;
    }
};