单链表反转

面试可能会面到,而且有的题目也需要单链表反转后,做得才比较机智,所以先自己搞一下单链表的反转

#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
struct ListNode
{
    int val;
    ListNode *next;
};
ListNode *head,*a,*b,*lst;
ListNode* ReverseSinglyListNode(ListNode* head)
{
    ListNode *tmp = NULL;
    ListNode *p = NULL;
    if (head == NULL)
    {
        return NULL;
    }
    tmp = head;
    while (tmp->next != NULL)
    {
        p = tmp->next;
        tmp->next = p->next;
        p->next = head;
        head = p;
    }
    return head;
}
int main()
{
    head = (ListNode*)malloc(sizeof(ListNode));
    a = (ListNode*)malloc(sizeof(ListNode));
    head->val = 1;
    head->next = NULL;
    a = head;
    lst = head;
    for(int i=0; i<4; i++)
    {
        b = (ListNode*)malloc(sizeof(ListNode));
        b->val = i+2;
        b->next = NULL;
        a->next = b;
        a = a->next;
    }
    head = ReverseSinglyListNode(head);
    while(head != NULL)
    {
        cout<<head->val<<" ";
        head = head->next;
    }
    return 0;
}


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