逆转单链表

问题

思路

cur = pre->next;
post = cur=>next;
cur->next = pre;
cur = post;

代码 

ListNode* reverseList(ListNode *root)
{
    if (root == NULL)
        return root;
    ListNode *cur = root;
    ListNode *pre = NULL;
    ListNode *post = NULL;
    ListNode *revRoot = NULL;
    while (cur != NULL)
    {
        post = cur->next;
        if (post == NULL)
            revRoot = cur;
        cur->next = pre;
        pre = cur;
        cur = post;
    }
    return revRoot;
}

完整执行

#include <iostream>
using namespace std;
struct ListNode
{
    int val;
    ListNode *next;
    ListNode(int v) : val(v), next(NULL) {}
};

ListNode* createList()
{
    ListNode *root = new ListNode(0);
    ListNode *p1 = new ListNode(1);
    ListNode *p2 = new ListNode(2);
    ListNode *p3 = new ListNode(3);
    root->next = p1;
    p1->next = p2;
    p2->next = p3;
    return root;
}

ListNode* reverseList(ListNode *root)
{
    if (root == NULL)
        return root;
    ListNode *cur = root;
    ListNode *pre = NULL;
    ListNode *post = NULL;
    ListNode *revRoot = NULL;
    while (cur != NULL)
    {
        post = cur->next;
        if (post == NULL)
            revRoot = cur;
        cur->next = pre;
        pre = cur;
        cur = post;
    }
    return revRoot;
}

void deleteList(ListNode *root)
{
    ListNode *p = root;
    while(root != NULL)
    {
        p = root->next;
        delete(root);
        root = p;
    }
}

void tranverse(ListNode* root)
{
    while(root != NULL)
    {
        cout << root->val << " ";
        root = root->next;
    }
    cout << endl;
}

int main()
{

    ListNode *root = createList();

    tranverse(root);
    root = reverseList(root);
    tranverse(root);
     
    deleteList(root);
}

结果

0 1 2 3 
3 2 1 0