如何将此 JavaScript 代码转换为 C++

Question

问题是 return 给定数组中的任何一个组合总和达到目标。我是 C++ 的新手。如何完成下面的函数 howSum() ？我不能在这里 return null 因为 return 类型是向量。我也无法传递向量。

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
        }
    }
}

Answer 1

让你的函数 return 一个布尔值来指示向量结果（return 作为输出参数）是否有效。无论如何，将数组（向量）作为输出参数引用传递可能比作为 return 值更有效。（虽然现在现代编译器可以做一些惊人的优化。）

bool howSum(int targetSum, const std::vector<int>& numbers, std::vector<int>& result)
{
    result.clear();

    if (targetSum == 0) {
        return true;
    }

    if (targetSum < 0) {
        return false;
    }

    for (int num : numbers) {
        const int remainder = targetSum - num;
        bool recursion_result = howSum(remainder, numbers, result);
        if (recursion_result) {
            result.push_back(num);
            return true;
        }
    }
    return false;
}

Answer 2

您可以使用 C++17 std::optional 和 return std::nullopt 当它不包含值时。

#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;
}

如何将此 JavaScript 代码转换为 C++

How to convert this JavaScript code to C++

c++

recursion

vector

data-structures