B04 Mnożenie

#include <bits/stdc++.h>

using namespace std;

void print(const vector<int>& v){
    for(int i = 0; i < v.size(); ++i){
        cerr<<v[i];
    }
}

void println(const vector<int>& v){
    print(v);
    cerr<<endl;
}

void outprint(const vector<int>& v){
    for(int i = 0; i < v.size(); ++i){
        cout<<v[i];
    }
}

void outprintln(const vector<int>& v){
    outprint(v);
    cout<<endl;
}

int suma_cyfr(vector<int> v){
    int suma = 0;
    for(int t : v){
        suma += t;
    }

    return suma;
}

vector<int> mult(vector<int>, vector<int>);

int main()
{
    int z;
    cin>>z;

    for(int i = 0; i < z; ++i){
        string sa, sb;
        cin>>sa;
        cin>>sb;

        int temp = 0;
        if(sa[0] == '-'){
            sa = sa.substr(1, sa.length()-1);
            temp++;
        }
        if(sb[0] == '-'){
            sb = sb.substr(1, sb.length()-1);
            temp++;
        }

        vector<int> a(sa.length());
        vector<int> b(sb.length());

        for(int i = 0; i < a.size(); ++i)
            a[i] = sa[i] - '0';
        for(int i = 0; i < b.size(); ++i)
            b[i] = sb[i] - '0';

        vector<int> p = mult(a, b);

        if(temp % 2 == 1 && suma_cyfr(p) > 0){
            cout<<"-";
        }
        outprintln(p);
    }
    return 0;
}

vector<int> add(vector<int> a, vector<int> b){
    while(a.size() > b.size())
        b.push_back(0);
    while(a.size() < b.size())
        a.push_back(0);

    vector<int> sum;

    int carry = 0;
    for(int i = 0; i < a.size(); ++i){
        b.push_back(0);
        int digit = a[i] + b[i] + carry;
        carry = digit / 10;
        digit = digit % 10;
        sum.push_back(digit);
    }

    return sum;
}

vector<int> mult(vector<int> a, vector<int> b){
    vector<int> product;

    reverse(a.begin(), a.end());
    reverse(b.begin(), b.end());

    vector<vector<int>> to_add;

    for(int i = 0; i < a.size(); ++i){
        vector<int> row;
        //cerr<<">> row "<<i<<" <<"<<endl;

        int carry = 0;
        for(int j = 0; j < b.size(); ++j){
            int digit = a[i] * b[j] + carry;
            carry = digit / 10;
            digit = digit % 10;
            //cerr<<" j: "<<j<<" | a[i]: "<<a[i]<<" b[j]: "<<b[j]<<" | carry: "<<carry<<" digit: "<<digit<<endl;

            row.push_back(digit);
        }
        if(carry != 0) row.push_back(carry);

        int row_offset = i;
        for(int j = 0; j < row_offset; ++j){
            row.insert(row.begin(), 0);
        }
        //cerr<<"row value (backwards): ";
        //println(row);
        to_add.push_back(row);
    }
    //cerr<<"\n------------------------------------------\n"<<endl;
    //cerr<<">>>> ADDING UP THE ROWS <<<<"<<endl;
    for(vector<int> t : to_add){
        //cerr<<"adding row \"";
        //print(t);
        //cerr<<"\":"<<endl;
        product = add(product, t);
        //cerr<<"TOTAL PRODUCT: ";
        //println(product);
    }

    while(product.back() == 0 && product.size() > 1)
        product.pop_back();

    reverse(product.begin(), product.end());
    return product;
}