string 也可以sort？！

#include<iostream>
#include<string>
#include<algorithm>
using namespace std;
string alphas,betas,numerics,others;
char c;
int main(){
    while(cin>>c){
        if(c>=48&&c<=57)numerics.append(1,c);
        else if(c>=65&&c<=90)betas.append(1,c);
        else if(c>=97&&c<=122)alphas.append(1,c);
        else others.append(1,c);
    }
    sort(alphas.begin(),alphas.end());
    sort(betas.begin(),betas.end());
    sort(numerics.begin(),numerics.end());
    sort(others.begin(),others.end());
    cout<<alphas<<betas<<numerics<<others;
    return 0;
}