c++ - 如何将此 JavaScript 代码转换为 C++

Question

问题是从给定数组中返回任何一个组合，总和为目标。我是 C++ 新手。如何完成下面的函数howSum()？我不能在这里返回 null，因为返回类型是向量。另外我在传递向量时遇到了麻烦。

JavaScript：

const howSum = (targetSum, numbers) => {
    if (targetSum === 0) return [];
    if (targetSum < 0) return null;

    for (let num of numbers) {
        const remainder = targetSum - num;
        const remainderResult = howSum(remainder, numbers);
        if (remainderResult !== null) 
        {
            return [...remainderResult, num];
        }
    }
    return null;
};

C++：

vector<int> howSum(int targetSum, vector<int> numbers)
{
    if(targetSum == 0) return {};
    if(targetSum < 0) return; //can't return null here in C++
    for (int i = 0; i < numbers.size(); i++)
    {
        int remainder = targetSum - numbers[i];
        vector<int> remainderResult = howSum(remainder, numbers);
        if(pass)
        {
            pass
        }
    }
}

标签： c++recursionvectordata-structures

Answer 1

您可以使用 C++17std::optional并std::nullopt在它不包含值时返回。

#include <optional>
#include <vector>

std::optional<std::vector<int>> 
howSum(int targetSum, const std::vector<int>& numbers) {
  if (targetSum == 0) 
    return std::vector<int>{};
  if (targetSum < 0) 
    return std::nullopt;
  for (auto numer : numbers) {
    const auto remainder = targetSum - numer;
    auto remainderResult = howSum(remainder, numbers);
    if (remainderResult) {
      remainderResult->push_back(targetSum);
      return remainderResult;
    }
  }
  return std::nullopt;
}