常规做法

https://ac.nowcoder.com/acm/contest/95700/H

#include <cstdio>
#include <iostream>
#include <string>
#include <cstring>
#include <cmath>
#include <algorithm>

using namespace std;
using ll = long long int;

int main()
{
    string str;
    getline(cin,str);

    for(char &a : str)
    {
        if(a<'Z'&& a>='A') a = (a+1)%65;
        else if(a=='Z') a = 'A';
        else if(a<='z'&&a>'a') a = a-1;
        else if(a =='a') a = 'z';
    }
    cout << str;

    return 0;
}

ch  = 'A' + (ch-'A'+1)%26; 后推
ch = 'z' - ('z'-ch+1)%26; 前推 
//规律就是 去掉%26 后 是+1就后推 是-1就前推 然后再加上取模