题解 | #Powerful Calculator#

#include <iostream>
#include <vector>
using namespace std;
void print(vector<int> &res){
    for(int i=res.size()-1;i>=0;i--)
        cout<<res[i];
    cout<<endl;
}
vector<int> add(vector<int> &A,vector<int> &B){
    int t=0;
    vector<int> C;
    for(int i=0;i<A.size()||i<B.size();i++){
        if(i<A.size()) t+=A[i];
        if(i<B.size()) t+=B[i];
        C.push_back(t%10);
        t/=10;
    }
    if(t) C.push_back(t);
    return C;//个十百千万...
}
//判断A>=B?
bool cmp(vector<int> &A,vector<int> &B){
    if(A.size()!=B.size()) return A.size()>B.size();
    for(int i=A.size()-1;i>=0;i--){//从最高位开始比较
        if(A[i]!=B[i])
            return A[i]>B[i];
    }
    return true;//A==B
}
vector<int> sub(vector<int> &A,vector<int> &B){
    int t=0;//向高位借位
    vector<int> C;
    for(int i=0;i<A.size();i++){
        t=A[i]-t;
        if(i<B.size()) t-=B[i];
        C.push_back((t+10)%10);
        if(t<0) t=1;
        else t=0;
    }
    //去除前导零
    while(C.size()>1&&C.back()==0) C.pop_back();
    return C;
}
vector<int> mul(vector<int> &A,vector<int> &B){
    vector<int> C(A.size()+B.size(),0);
    for(int i=0;i<A.size();i++){
        for(int j=0;j<B.size();j++){
            C[i+j]+=A[i]*B[j];
        }
    }
    for(int i=0;i+1<C.size();i++){
        C[i+1]+=C[i]/10;
        C[i]%=10;
    }
    //去除前导零
    while(C.size()>1&&C.back()==0) C.pop_back();
    return C;
}
int main() {
    string a,b;
    while(cin>>a>>b){
        vector<int> A,B;
        for(int i=a.size()-1;i>=0;i--) A.push_back(a[i]-'0');//个十百千万...
        for(int i=b.size()-1;i>=0;i--) B.push_back(b[i]-'0');
        vector<int> res;
        res=add(A,B);
        print(res);
        if(cmp(A,B)){
            res=sub(A,B);
        }else{
            cout<<"-";
            res=sub(B,A);
        }
        print(res);
        res=mul(A,B);
        print(res);
    }
    return 0;
}