a times b

#include <iostream>
#include <string>
#include <algorithm>

using namespace std;

// Helper function to add two large numbers represented as strings
string addLargeNumbers(const string &num1, const string &num2) {
    int carry = 0;
    string result;
    int n1 = num1.size(), n2 = num2.size();
    int maxLength = max(n1, n2);

    for (int i = 0; i < maxLength || carry; i++) {
        int digit1 = i < n1 ? num1[n1 - i - 1] - '0' : 0;
        int digit2 = i < n2 ? num2[n2 - i - 1] - '0' : 0;
        int sum = digit1 + digit2 + carry;
        result.push_back(sum % 10 + '0');
        carry = sum / 10;
    }
    reverse(result.begin(), result.end());
    return result;
}

// Helper function to subtract two large numbers represented as strings
string subtractLargeNumbers(const string &num1, const string &num2) {
    string result;
    int n1 = num1.size(), n2 = num2.size();
    int carry = 0;

    for (int i = 0; i < n1; i++) {
        int digit1 = num1[n1 - i - 1] - '0';
        int digit2 = i < n2 ? num2[n2 - i - 1] - '0' : 0;
        int diff = digit1 - digit2 - carry;
        if (diff < 0) {
            diff += 10;
            carry = 1;
        } else {
            carry = 0;
        }
        result.push_back(diff + '0');
    }

    while (result.size() > 1 && result.back() == '0') {
        result.pop_back();
    }
    reverse(result.begin(), result.end());
    return result;
}

// Pad a number with zeros at the end
string padZeros(const string &num, int zeros) {
    return num + string(zeros, '0');
}

// Karatsuba multiplication for large numbers represented as strings
string karatsubaMultiply(const string &num1, const string &num2) {
    int n = max(num1.size(), num2.size());
    if (n == 1) {
        int product = (num1[0] - '0') * (num2[0] - '0');
        return to_string(product);
    }

    int half = n / 2;
    string a = num1.substr(0, num1.size() - half);
    string b = num1.substr(num1.size() - half);
    string c = num2.substr(0, num2.size() - half);
    string d = num2.substr(num2.size() - half);

    string ac = karatsubaMultiply(a, c);
    string bd = karatsubaMultiply(b, d);
    string ab_plus_cd = karatsubaMultiply(addLargeNumbers(a, b), addLargeNumbers(c, d));
    string middleTerm = subtractLargeNumbers(ab_plus_cd, addLargeNumbers(ac, bd));

    return addLargeNumbers(addLargeNumbers(padZeros(ac, 2 * half), padZeros(middleTerm, half)), bd);
}

int main() {
    string a, b;
    cin >> a >> b;
    cout << karatsubaMultiply(a, b) << endl;
    return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: WRONG ANSWER

Test 8

Verdict: ACCEPTED

Test 9

Verdict: WRONG ANSWER

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: WRONG ANSWER

Test 14

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::substr: __pos (which is 18446744073709551615) > this->size() (which is 0)

Test 15

Verdict: WRONG ANSWER

Test 16

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::substr: __pos (which is 18446744073709551615) > this->size() (which is 1)

Test 17

Verdict: WRONG ANSWER

Test 18

Verdict: WRONG ANSWER

Test 19

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::substr: __pos (which is 18446744073709551615) > this->size() (which is 1)

Test 20

Verdict: WRONG ANSWER

Test 21

Verdict: WRONG ANSWER

Test 22

Verdict: WRONG ANSWER

Test 23

Verdict: WRONG ANSWER

Test 24

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::substr: __pos (which is 18446744073709551615) > this->size() (which is 0)

Test 25

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::substr: __pos (which is 18446744073709551614) > this->size() (which is 0)

Test 26

Verdict: WRONG ANSWER

Test 27

Verdict: WRONG ANSWER

Test 28

Verdict: WRONG ANSWER

Test 29

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::substr: __pos (which is 18446744073709551615) > this->size() (which is 2)

Test 30

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::substr: __pos (which is 18446744073709551615) > this->size() (which is 3)

Test 31

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::substr: __pos (which is 18446744073709551613) > this->size() (which is 19)

Test 32

Verdict: WRONG ANSWER

Test 33

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::substr: __pos (which is 18446744073709551610) > this->size() (which is 3)

Test 34

Verdict: WRONG ANSWER

Test 35

Verdict: WRONG ANSWER

Test 36

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::substr: __pos (which is 18446744073709551613) > this->size() (which is 6)

Test 37

Verdict: WRONG ANSWER

Test 38

Verdict: WRONG ANSWER

Test 39

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::substr: __pos (which is 18446744073709551589) > this->size() (which is 8)

Test 40

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::substr: __pos (which is 18446744073709551604) > this->size() (which is 10)

Test 41

Verdict: WRONG ANSWER

Test 42

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::substr: __pos (which is 18446744073709551602) > this->size() (which is 33)

Test 43

Verdict: WRONG ANSWER

Test 44

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::substr: __pos (which is 18446744073709551570) > this->size() (which is 2)

Test 45

Verdict: WRONG ANSWER

Test 46

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::substr: __pos (which is 18446744073709551488) > this->size() (which is 21)

Test 47

Verdict: WRONG ANSWER

Test 48

Verdict: WRONG ANSWER

Test 49

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::substr: __pos (which is 18446744073709551551) > this->size() (which is 238)

Test 50

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::substr: __pos (which is 18446744073709551584) > this->size() (which is 83)

Test 51

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::substr: __pos (which is 18446744073709551389) > this->size() (which is 179)

Test 52

Verdict: WRONG ANSWER

Test 53

Verdict: WRONG ANSWER

Test 54

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::substr: __pos (which is 18446744073709551440) > this->size() (which is 76)

Test 55

Verdict: WRONG ANSWER

Test 56

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::substr: __pos (which is 18446744073709551288) > this->size() (which is 373)

Test 57

Verdict: TIME LIMIT EXCEEDED

Test 58

Verdict: TIME LIMIT EXCEEDED

Test 59

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::substr: __pos (which is 18446744073709547504) > this->size() (which is 19562)

Test 60

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::substr: __pos (which is 18446744073709546085) > this->size() (which is 29444)