問題是從給定陣列中回傳與目標相加的任何一種組合。我是 C 的新手。請幫我完成下面的函式howSum()。我不能在這里回傳 null 因為回傳型別是向量。我也無法傳遞向量。
//Java腳本
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
}
}
}
uj5u.com熱心網友回復：
您可以使用 C 17std::optional并std::nullopt在它不包含值時回傳。
#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;
}
uj5u.com熱心網友回復：
讓您的函式回傳一個 bool 以指示向量結果（作為輸出引數回傳）是否有效。無論如何，將陣列（向量）作為輸出引數參考傳遞可能比作為回傳值傳遞更有效。（盡管如今現代編譯器可以進行一些驚人的優化。）
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;
}
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