c++

include

using namespace std;

char decode(char m,char k){

int d;

if(k>='a')d=k-'a';

else d=k-'A';

if(m>='a'){

    m-=d;

    if(m<'a')m+=26;

}else{

    m-=d;

    if(m<'A')m+=26;

}

return m;

}

string sk,s;

int main() {

cin>>sk>>s;

int ind=0;

for(int i=0;i<s.size();i++){

    cout<<decode(s[i],sk[ind]);

    ind=(ind+1)%sk.size();

}

return 0;

}

运行:{ ||abcdefghijklmnopqrstuvwxyz||

zzzzzzzzzzzzzzzzzzzzzzzzzz

zyxwvutsrqponmlkjihgfedcba

zxvtrpnljhfdbzxvtrpnljhfdb

zwtqnkhebyvspmjgdaxurolifc

zvrnjfbxtplhdzvrnjfbxtplhd

zupkfavqlgbwrmhcxsnidytoje

ztnhbvpjdxrlfztnhbvpjdxrlf

zslexqjcvohatmfyrkdwpibung

zrjbtldvnfxphzrjbtldvnfxph

zqhypgxofwnevmdulctkbsjari

zpfvlbrhxndtjzpfvlbrhxndtj

zodshwlapetixmbqfujyncrgvk

znbpdrfthvjxlznbpdrfthvjxl

zmzmzmzmzmzmzmzmzmzmzmzmzm

zlxjvhtfrdpbnzlxjvhtfrdpbn

zkvgrcnyjufqbmxitepalwhsdo

zjtdnxhrblvfpzjtdnxhrblvfp

zirajsbktcludmvenwfoxgpyhq

zhpxfnvdltbjrzhpxfnvdltbjr

zgnubipwdkryfmtahovcjqxels

zflrxdjpvbhntzflrxdjpvbhnt

zejotydinsxchmrwbglqvafkpu

zdhlptxbfjnrvzdhlptxbfjnrv

zcfiloruxadgjmpsvybehknqtw

zbdfhjlnprtvxzbdfhjlnprtvx

zabcdefghijklmnopqrstuvwxy

zzzzzzzzzzzzzzzzzzzzzzzzzz

|| || }