【剑指**】25.合并两个排序的链表

25.合并两个排序的链表

题目描述

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。

思路分析

特殊条件考虑全面即可，整体做法不难

代码

/*
struct ListNode {
    int val;
    struct ListNode *next;
    ListNode(int x) :
            val(x), next(NULL) {
    }
};*/
class Solution {
public:
    ListNode* Merge(ListNode* pHead1, ListNode* pHead2)
    {
        if (pHead1 == NULL) return pHead2;
        if (pHead2 == NULL) return pHead1;
        ListNode* new_head = NULL;
        ListNode* p = NULL;
        if (pHead1->val < pHead2->val) {
            new_head = pHead1;
            pHead1 = pHead1->next;
        }
        else {
            new_head = pHead2;
            pHead2 = pHead2->next;
        }
        p = new_head;
        while (pHead1 != NULL && pHead2 != NULL) {
            if (pHead1->val < pHead2->val) {
                p->next = pHead1;
                pHead1 = pHead1->next;
            }
            else {
                p->next = pHead2;
                pHead2 = pHead2->next;
            }
            p = p->next;
        }
        if (pHead1 != NULL) {
            p->next = pHead1;
        }
        if (pHead2 != NULL) {
            p->next = pHead2;
        }
        return new_head;
    }
};