int_as_array_multiply.cc

#include <algorithm>
#include <cstdlib>
#include <vector>

#include "test_framework/generic_test.h"

using std::abs;
using std::vector;

vector<int> Multiply(vector<int> num1, vector<int> num2) {
  const int sign = (num1.front() < 0) ^ (num2.front() < 0) ? -1 : 1;
  num1.front() = abs(num1.front()), num2.front() = abs(num2.front());

  vector<int> result(size(num1) + size(num2), 0);
  for (int i = size(num1) - 1; i >= 0; --i) {
    for (int j = size(num2) - 1; j >= 0; --j) {
      result[i + j + 1] += num1[i] * num2[j];
      result[i + j] += result[i + j + 1] / 10;
      result[i + j + 1] %= 10;
    }
  }

  // Remove the leading zeroes.
  result = {
      find_if_not(begin(result), end(result), [](int a) { return a == 0; }),
      end(result)};
  if (empty(result)) {
    return {0};
  }
  result.front() *= sign;
  return result;
}

int main(int argc, char* argv[]) {
  std::vector<std::string> args{argv + 1, argv + argc};
  std::vector<std::string> param_names{"num1", "num2"};
  return GenericTestMain(args, "int_as_array_multiply.cc",
                         "int_as_array_multiply.tsv", &Multiply,
                         DefaultComparator{}, param_names);
}