#include<iostream>  
#include<string>  
#include<algorithm>  
using namespace std;  
int n;  
bool judge(string s1,string s2,string s3)  
{  
    reverse(s1.begin(),s1.end());  
    bool flag=true;  
    for(int i=0;i<n;i++){  
        if(((s2[i]-'a'+s3[i]-'a')-2*(s1[i]-'a'))%26!=0){  
            flag=false;  
            break;  
        }  
    }  
    return flag;  
}  
int main()  
{  
    string s1,s2,s3;  
    cin>>n;  
    cin>>s1>>s2>>s3;  
    if(judge(s1,s2,s3)) reverse(s1.begin(),s1.end()),cout<<s1<<endl;  
    else if(judge(s2,s1,s3)) reverse(s2.begin(),s2.end()),cout<<s2<<endl;  
    else if(judge(s3,s2,s1))reverse(s3.begin(),s3.end()),cout<<s3<<endl;  
    return 0;  
}

下面是自己写的，感觉虽然思路一样，但是写的就丑了许多

#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;
    string s[4];
    cin>>n>>s[1]>>s[2]>>s[3];
    //cout<<s[1]<<s[2]<<s[3];
    for(int i=1;i<=3;i++){
        string sub(n,'0');
        for(int k=0;k<n;k++){
            sub[k]=s[i][n-1-k];
        }
        //cout<<sub<<endl;
        if(i==1){
            bool flag = true;
            for(int k=0;k<n;k++){
                if(abs((s[2][k]-'a')-(sub[k]-'a'))%26!=abs((s[3][k]-'a')-(sub[k]-'a'))%26&&
                (abs((s[2][k]-'a')-(sub[k]-'a'))%26+abs((s[3][k]-'a')-(sub[k]-'a'))%26)!=26) flag = false; 
            }
            if(flag==true){
                cout<<sub<<endl;
                break;
            } 
        }
        else if(i==2){
            bool flag = true;
            for(int k=0;k<n;k++){
                if(abs((s[1][k]-'a')-(sub[k]-'a'))%26!=abs((s[3][k]-'a')-(sub[k]-'a'))%26&&
                (abs((s[1][k]-'a')-(sub[k]-'a'))%26+abs((s[3][k]-'a')-(sub[k]-'a'))%26)!=26) flag = false;
            }
            if(flag==true){
                cout<<sub<<endl;
                break;
            } 
        }
        else if(i==3){
            bool flag = true;
            for(int k=0;k<n;k++){
                if(abs((s[2][k]-'a')-(sub[k]-'a'))%26!=abs((s[1][k]-'a')-(sub[k]-'a'))%26&&
                (abs((s[2][k]-'a')-(sub[k]-'a'))%26+abs((s[1][k]-'a')-(sub[k]-'a'))%26)!=26) flag = false;
            }
            if(flag==true){
                cout<<sub<<endl;
                break;
            } 
        }
    }
    return 0;
}