单链表倒置（递归与非递归）

#include <iostream>
using namespace std;

#include <stdio.h>

struct Node {
    int data;
    Node * next;
};
// 非递归
Node * Reverse(Node * first)
{
    Node *p = first, *q, *r;
    if (p == NULL)
        return p;
    r = p->next;
    p->next = NULL;
    while (r != NULL) {
        q = r;
        r = r->next;
        q->next = p;
        p = q;
    }
    
    return q;    
}

// 递归
Node * Reverse2(Node * first)
{
    if (first == NULL || first->next == NULL)
        return first;
    Node * p = Reverse2(first->next);
    first->next->next = first;
    first->next = NULL;
    return p;
}

Node * Construct()
{
    Node * node = NULL, *first;
    int n;
    scanf("%d", &n);
    if (n == 0)
        return NULL;
    
    node = new Node;
    node->data = n;
    node->next = NULL;
    first = node;
    
    while (scanf("%d", &n) && n != 0) {
        node->next = new Node;
        node->next->data = n;
        node->next->next = NULL;
        node = node->next;
    }
    
    return first;
}

void Print(Node * first)
{
    while (first != NULL) {
        printf("%3d", first->data);
        first = first->next;
    }
    printf("\n");
}

int main()
{
    Node * first = Construct();
    Print(first);
    Print(first = Reverse(first));
    Print(first = Reverse2(first));
    Print(first = Reverse2(first));
    Print(first = Reverse2(first));
    return 0;
}