无法让 min_element 在 C++ 中工作

Question

我正在编写一个小型递归算法。代码如下：

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

vector<int> coins;

int checkchange(int left) {
    vector<int> choices (coins.size());
    if (left == 0)
        return 0;
    else {
        int min;
        for (int i=0;i<coins.size();i++) {
            choices.at(i) = (1 + checkchange(left - coins.at(i)));
        }
        return min_element(choices.front(),choices.back());
    }
}


int main() {
    int N;
    cin >> N;
    for (int i=0;i<N;i++) {
        int c,m,temp,change;
        cin >> c >> m;
        for (int j=0;j<c;j++) {
            cin >> temp;
            coins.push_back(temp);
        }

        for (int j=0;j<m;j++) {
            cin >> temp;
            change = checkchange(temp);
            cout << change;
        }
    }
    return 0;
}

我收到以下错误：

在
中包含的文件中 /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/algorithm:62,
从burningcoins.cpp：3：/usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_algo.h：
在函数'_FIter std::min_element(_FIter, _FIter) [with _FIter =
int]'：burningcoins.cpp:19：从这里实例化
/usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_algo.h:5998:
错误：“一元 *”的类型参数无效
/usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/stl_algo.h:5998:
错误：“一元 *”的类型参数无效

我试过用 g++ 和 gcc 编译，都给我同样的错误。我做错了什么？

编辑：

新代码：

int checkchange(int left) {
    vector<int> choices (coins.size());
    if (left == 0)
        return 0;
    else {
        for (int i=0;i<coins.size();i++) {
            choices[i] = (1 + checkchange(left - coins.at(i)));
        }
        return *min_element(choices.begin(), choices.end());
    }
}

新的错误信息：

/tmp/ccV3VLsK.o：在函数main': <br/> burningcoins.cpp:(.text+0x16a): undefined reference tostd::cin'
Burningcoins.cpp:(.text+0x16f): 未定义对std::basic_istream<char, std::char_traits<char> >::operator>>(int&)' <br/> burningcoins.cpp:(.text+0x187): undefined reference tostd::cin'
的引用 Burningcoins.cpp:(.text+0x18c): 未定义引用std::basic_istream<char, std::char_traits<char> >::operator>>(int&)' <br/> burningcoins.cpp:(.text+0x19b): undefined reference tostd::basic_istream >::operator>>(int&)'
burncoins.cpp:(.text+0x1b0): 未定义引用std::cin' <br/> burningcoins.cpp:(.text+0x1b5): undefined reference tostd::basic_istream >::operator>>(int&)'
Burningcoins.cpp:(.text+0x1ec): 未定义引用 std::cin' <br/> burningcoins.cpp:(.text+0x1f1): undefined reference tostd::basic_istream >::operator>>(int&)'
Burningcoins.cpp:(.text+0x208): 未定义引用std::cout' <br/> burningcoins.cpp:(.text+0x20d): undefined reference tostd::basic_ostream >::operator /tmp/ccV3VLsK.o：在函数__static_initialization_and_destruction_0(int, int)': <br/> burningcoins.cpp:(.text+0x261): undefined reference tostd::ios_base::Init::Init()'
burncoins.cpp:(.text+0x266): undefined reference to std::ios_base::Init::~Init()' <br/> /tmp/ccV3VLsK.o: In functionstd::vector >::_M_range_check(unsigned long) const':
burncoins.cpp:(.text._ZNKSt6vectorIiSaIiEE14_M_range_checkEm[std::vector >::_M_range_check(unsigned long) const]+0x2d): 未定义引用std::__throw_out_of_range(char const*)' <br/> /tmp/ccV3VLsK.o: In functionstd::vector >::_M_insert_aux(__gnu_cxx::__normal_iterator >>, int const&)':
burncoins.cpp:(.text._ZNSt6vectorIiSaIiEE13_M_insert_auxEN9__gnu_cxx17__normal_iteratorIPiS1_EERKi[std::vector >::_M_insert_aux(__gnu_cxx::__normal_iterator >>, int const&)]+0x259): 未定义引用__cxa_begin_catch' <br/> burningcoins.cpp:(.text._ZNSt6vectorIiSaIiEE13_M_insert_auxEN9__gnu_cxx17__normal_iteratorIPiS1_EERKi[std::vector<int, std::allocator<int> >::_M_insert_aux(__gnu_cxx::__normal_iterator<int*, std::vector<int, std::allocator<int> > >, int const&)]+0x2be): undefined reference to__'cxa_rethrow burncoins.cpp:(.text._ZNSt6vectorIiSaIiEE13_M_insert_auxEN9__gnu_cxx17__normal_iteratorIPiS1_EERKi[std::vector >::_M_insert_aux(__gnu_cxx::__normal_iterator > >, int const&)]+0x2c8): 未定义引用__cxa_end_catch' <br/> /tmp/ccV3VLsK.o: In functionstd::vector >:: long, char const*) const':
burncoins.cpp:(.text._ZNKSt6vectorIiSaIiEE12_M_check_lenEmPKc[std::vector >::_M_check_len(unsigned long, char const*) const]+0x4c): 未定义引用std::__throw_length_error(char const*)' <br/> /tmp/ccV3VLsK.o: In function__gnu_cxx::new_allocator::deallocate(int*, unsigned长）'：
burncoins.cpp:(.text._ZN9__gnu_cxx13new_allocatorIiE10deallocateEPim[__gnu_cxx::new_allocator::deallocate(int*, unsigned long)]+0x1c): 未定义引用operator delete(void*)' <br/> /tmp/ccV3VLsK.o: In function__gnu_cxx::new_allocator::allocate(unsigned long, void const*) '：
burncoins.cpp:(.text._ZN9__gnu_cxx13new_allocatorIiE8allocateEmPKv[__gnu_cxx::new_allocator::allocate(unsigned long, void const*)]+0x35): 未定义引用std::__throw_bad_alloc()' <br/> burningcoins.cpp:(.text._ZN9__gnu_cxx13new_allocatorIiE8allocateEmPKv[__gnu_cxx::new_allocator<int>::allocate(unsigned long, void const*)]+0x45): undefined reference tooperator new(unsigned long)'
/tmp/ccV3VLsK.o:(.eh_frame+0x12): 未定义引用 __gxx_personality_v0' <br/> /tmp/ccV3VLsK.o:(.eh_frame+0x4f): undefined reference to__gxx_personality_v0'
collect2: ld 返回 1 个退出状态

Answer 1

std::min_element 取一个范围。 front 和 back 返回对实际值的引用。您应该使用 begin 和 end 方法将迭代器返回到向量中的相应位置：

min_element(choices.begin(), choices.end());
//                  ^^^^^            ^^^

如果您觉得这很乏味，您可以创建一个环绕标准 min_element 的函数：

template <class Container>
auto min_element(Container c) -> decltype(std::min_element(c.begin(), c.end()))
{
    return std::min_element(c.begin(), c.end());
}

并将其用作：

min_element(choices);