题解 | MP3光标位置

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

int main() {
    int num;
    string commands;
    cin >> num >> commands;
    int start = 1, end = 4;
    int cur = 1;
    for(const char& c: commands) {
        if(c == 'U') {
            if(cur == 1) {
                cur = num;
                start = num - 3;
                end = num;
            } else {
                --cur;
                if(end - cur > 3) {
                    --end;
                    --start;
                }
            }
        } 
        else {
            if(cur == num) {
                cur = 1;
                start = 1;
                end = 4;
            } else {
                ++cur;
                if(cur - start > 3) {
                    ++start;
                    ++end;
                }
            }
        }
    }
    if(num <= 4) {
        for(int i = 1; i <= num; ++i) {
            cout << i << " ";
        }
        cout << endl;
        cout << cur;
        return 0;
    }

    for(int i = start; i <= end; ++i) {
        cout << i << " ";
    }
    cout << endl;
    cout << cur;
    return 0;
}