C++高精度乗算テンプレート大数乗算高精度乗算低精度|高精度乗算高精度

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高精度x低精度

高精度x高精度

高精度x低精度

#include 
#include 

using namespace std;

vector <int> mul(vector <int> & A, int b) {
    vector <int> C;

    int t = 0;
    for (int i = 0; i < A.size(); i ++) {
        t += A[i] * b;       // t + A[i] * b = 7218
        C.push_back(t % 10); //      8
        t /= 10;             // 721      
    }
    
    while (t) {            //         t
        C.push_back(t % 10);
        t /= 10;
    }
    
    while (C.size() > 1 && C.back() == 0) C.pop_back();
    
    return C;
}

int main() {
    string a;
    int b;
    cin >> a >> b;

    vector <int> A;
    for (int i = a.size() - 1; i >= 0; i --) A.push_back(a[i] - '0');

    auto C = mul(A, b);

    for (int i = C.size() - 1; i >= 0; i --) {
        cout << C[i];
    }

    return 0;
}

高精度x高精度

#include 
#include 

using namespace std;

vector<int> mul(vector<int> &A, vector<int> &B) {
    vector<int> C(A.size() + B.size(), 0); //      0， 999*99   5  

    for (int i = 0; i < A.size(); i++)
        for (int j = 0; j < B.size(); j++)
            C[i + j] += A[i] * B[j];

    int t = 0;
    for (int i = 0; i < C.size(); i++) { // i = C.size() - 1  t      10
        t += C[i];
        C[i] = t % 10;
        t /= 10;
    }

    while (C.size() > 1 && C.back() == 0) C.pop_back(); //        0，          0
    return C;
}

int main() {
    string a, b;
    cin >> a >> b; // a = "1222323", b = "2323423423"

    vector<int> A, B;
    for (int i = a.size() - 1; i >= 0; i--)
        A.push_back(a[i] - '0');
    for (int i = b.size() - 1; i >= 0; i--)
        B.push_back(b[i] - '0');

    auto C = mul(A, B);

    for (int i = C.size() - 1; i >= 0; i--)
        cout << C[i];

    return 0;
}