题解 | #MP3光标位置#

//C++实现，不借助容器，设定两个变量，一个是光标指向的歌曲数(1—歌曲总数)，另一个是光标在框内的的相对位置(1/2/3/4)
//得到这两个值就可以推导出框内的4首歌曲，代码如下，还可以更简介

#include<iostream>
using namespace std;
#include<string>

int main()
{
    int num;
    string str;
    while(cin>>num>>str)
    {
        int index=1;
        int len=str.length();
        int Up=0,Down=0;
        int pos=0;    //记录当前光标的位置
        if(num<=4)
        {
            for(int i=0;i<len;++i)
            {
                if(index==num&&str[i]=='D'){
                    index=1;
                }
                else if(index==1&&str[i]=='U'){
                    index=index-1+num;
                }
                else if(str[i]=='U'){
                    index--;
                }
                else if(str[i]=='D'){
                    index++;
                }
            }
            for(int i=1;i<=num;++i)
            {
                cout<<i<<" ";
            }
        }else
        {
            for(int i=0;i<len;++i)
            {
                if(index==num&&str[i]=='D'){
                    index=1;
                    pos=1;
                }
                else if(index==1&&str[i]=='U'){
                    index=num;
                    pos=4;
                }
                else if(str[i]=='U'){
                    index--;
                    if(pos!=1)    pos--;
                    else pos=1;
                }
                else if(str[i]=='D'){
                    index++;
                    if(pos!=4) pos++;
                    else pos=4;
                }
            }
            switch(pos)
            {
                case 1:
                    {
                        for(int i=index;i<index+4;++i)
                            cout<<i<<" ";
                        break;
                    }
                case 2:
                    {
                        for(int i=index-1;i<index+3;++i)
                            cout<<i<<" ";
                        break;
                    }
                case 3:
                    {
                        for(int i=index-2;i<index+2;++i)
                            cout<<i<<" ";
                        break;
                    }
                case 4:
                    {
                        for(int i=index-3;i<index+1;++i)
                            cout<<i<<" ";
                        break;
                    }
            }
        }
        cout<<endl<<index<<endl;
    }
    return 0;
}