hdu 2816(I Love You Too)(STL)

#include<stdio.h>
#include<map>
#include<string>
#include<iostream>
using namespace std;
map<string,char>ms;
map<char,char>mc;
string s1,s2,si;
int main()
{
    int t;
    ms["21"]='A';
    ms["22"]='B';
    ms["23"]='C';
    ms["31"]='D';
    ms["32"]='E';
    ms["33"]='F';
    ms["41"]='G';
    ms["42"]='H';
    ms["43"]='I';
    ms["51"]='J';
    ms["52"]='K';
    ms["53"]='L';
    ms["61"]='M';
    ms["62"]='N';
    ms["63"]='O';
    ms["71"]='P';
    ms["72"]='Q';
    ms["73"]='R';
    ms["74"]='S';
    ms["81"]='T';
    ms["82"]='U';
    ms["83"]='V';
    ms["91"]='W';
    ms["92"]='X';
    ms["93"]='Y';
    ms["94"]='Z';

    mc['Q']='A';
    mc['W']='B';
    mc['E']='C';
    mc['R']='D';
    mc['T']='E';
    mc['Y']='F';
    mc['U']='G';
    mc['I']='H';
    mc['O']='I';
    mc['P']='J';
    mc['A']='K';
    mc['S']='L';
    mc['D']='M';
    mc['F']='N';
    mc['G']='O';
    mc['H']='P';
    mc['J']='Q';
    mc['K']='R';
    mc['L']='S';
    mc['Z']='T';
    mc['X']='U';
    mc['C']='V';
    mc['V']='W';
    mc['B']='X';
    mc['N']='Y';
    mc['M']='Z';
    s1.clear();
    while(cin>>s1)
    {
        s2.clear();
        for(int i=0;i<s1.size();i=i+2)
        {
            si.clear();
            for(int j=i;j<i+2;j++)
            si+=s1[j];
            s2+=ms[si];
        }
        //cout<<s2<<endl;
        s1.clear();
        for(int i=0;i<s2.size();i++)
        s1+=mc[s2[i]];
        string s3,s4;//保存分的两段
        t=(s1.size()+1)/2;
        for(int i=0;i<t;i++)
        s3+=s1[i];
        for(int i=t;i<s1.size();i++)
        s4+=s1[i];
        //cout<<s3<<endl<<s4<<endl;
        s1.clear();
        for(int i=0;i<s3.size();i++)
        {
            s1+=s3[i];
            if(s4[i]!='\0')s1+=s4[i];
        }
        //cout<<s1<<endl;
        for(int i=s1.size()-1;i>=0;i--)
        cout<<s1[i];
        cout<<endl;
        s1.clear();
    }
    return 0;
}