题目
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)
{
if(nullptr == pHead1) return pHead2;
if(nullptr == pHead2) return pHead1;
//先找到链表中值最小的节点作为头结点，再一个一个将链表链接起来
ListNode *ret;
if(pHead1->val <= pHead2->val )
{
ret = pHead1;
pHead1 = pHead1->next;
}else{
ret = pHead2;
pHead2 = pHead2->next;
}
ListNode * head = ret;
while(pHead1 != nullptr && pHead2 != nullptr)
{
if(pHead1->val <= pHead2->val)
{
ret->next = pHead1;
ret = ret->next;
pHead1 = pHead1->next;
}
else{
ret->next = pHead2;
ret = ret->next;
pHead2 = pHead2->next;
}
}
if(pHead1 != nullptr)
{
ret->next = pHead1;
}
if(pHead2 != nullptr)
{
ret->next = pHead2;
}
return head;
}
};
