约瑟夫环问题

直接上C++代码：

这里有问题的地方就是joseph_circle.cpp实现方法eliminate的循环语句的条件，如果把p->next != p改为p->next != nullptr就会出现循环已经删除了最后一个还继续循环，还继续删除，然后抛出空指针异常。

joseph_circle.h

#ifndef __YueHeFuHuan__joseph_circle__
#define __YueHeFuHuan__joseph_circle__

#include <stdio.h>
#include <iostream>
using namespace std;
struct node{
    int payload;
    node* next;
    node(int value){
        payload = value;
    }//通过构造器传值更好，更直观。
};

class joseph_circle{
public:
    joseph_circle();
    node* tail;
    void add(int n);
    void output();
    void eliminate(int step);
};


#endif /* defined(__YueHeFuHuan__joseph_circle__) */

joseph_circle.cpp

#include "joseph_circle.h"

joseph_circle::joseph_circle(){
    tail = nullptr;
}
void joseph_circle::add(int value){
    if (tail == nullptr) {
        tail = new node(value);
        tail->next = tail;
    }else{
        node* next_node = tail->next;
        tail->next = new node(value);
        tail = tail->next;
        tail -> next = next_node;
        
    }
}
void joseph_circle::output(){
    if (tail == nullptr) {
        cout << "链表为空！" << endl;
    }else{
        node* p = tail->next;
        while (true) {
            cout << "payload:" << p->payload << endl;
            if (p == tail) {
                break;
            }
            p = p->next;
        }
    }
}
void joseph_circle::eliminate(int step){
    if (tail == nullptr) {
        cout << "链表为空！" << endl;
    }else{
        node* p = tail;
        node* delete_p;
        //事实证明，当delete一个指针之后，其指针指向不为空
        while (p != nullptr && p->next != p) {
                //根据步长找到目标元素
                for (int i=0; i<step-1; i++) {
                    p = p->next;
                }
                delete_p = p->next;
                cout << "deleting: " << delete_p->payload << endl;
                p->next = delete_p->next;
                if (delete_p == tail) {
                    tail = p;
                }
                delete delete_p;
            
            }
        }
}