Question

我正在尝试使用std：copy将3D数组复制到vector。

int myint[3][3][3] = { { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 } },
                       { { 11,12, 13 }, { 14, 15, 16 }, {17, 18, 19 } },
                       { { 21, 22, 23 }, { 24, 25, 26 }, { 27, 28, 29 } } };

int favint[3][3][3];

我可以如下将myint复制到favint

std::copy(&myint[0][0][0],
          &myint[0][0][0] + (sizeof(myint) / sizeof(*myint)) * (sizeof(*myint) / sizeof(**myint))*(sizeof(**myint) / sizeof(***myint)),
          &favint[0][0][0]);

我可以如下将myint复制到myvector：

vector<vector<vector<int> > > myvector;         
    for (int k = 0; k<sizeof(myint) / sizeof(*myint); k++)
    {
        myvector.push_back(vector<vector<int> >()); 
        for (int i = 0; i<sizeof(*myint) / sizeof(**myint); i++)
        {
            myvector[k].push_back(vector<int>()); 
            for (int j = 0; j<sizeof(**myint) / sizeof(***myint); j++)
            {                   
                myvector[k][i].push_back(myint[k][i][j]); 
            }
        }
    }

使用std :: copy将3D数组复制到3D数组很简单。如何使用std :: copy将myint复制到myvector？还有其他简单的方法吗？

Answer 1

您可能会做类似的事情：

std::vector<int> to_vector(const int (&a)[3])
{
    return {std::begin(a), std::end(a)};
}

std::vector<std::vector<int>> to_vector(const int (&a)[3][3])
{
    return {to_vector(a[0]), to_vector(a[1]), to_vector(a[2])};
}

std::vector<std::vector<std::vector<int>>> to_vector(const int (&a)[3][3][3])
{
    return {to_vector(a[0]), to_vector(a[1]), to_vector(a[2])};
}

对于通用（但编译时）值，template可能会有所帮助：

template <std::size_t N>
std::vector<int> to_vector(const int (&a)[N])
{
    return {std::begin(a), std::end(a)};
}

template <std::size_t N1, std::size_t N2>
auto to_vector(const int (&a)[N1][N2])
-> std::vector<std::vector<int>>
{
    std::vector<std::vector<int>> res;
    res.reserve(N1);
    for (const auto& inner_a : a) {
        res.push_back(to_vector(inner_a));
    }
    return res;
}

template <std::size_t N1, std::size_t N2, std::size_t N3>
auto to_vector(const int (&a)[N1][N2][N3])
-> std::vector<std::vector<std::vector<int>>>
{
    std::vector<std::vector<std::vector<int>>> res;
    res.reserve(N1);
    for (const auto& inner_a : a) {
        res.push_back(to_vector(inner_a));
    }
    return res;
}

Demo

Answer 2

只需使用import java.util.Scanner; public class RomanNumerals { public static String convert(int n) { String roman = ""; if ((n >= 0) && (n <= 3999)) { int thousand = (n / 1000); int hundred = (n % 1000) / 100; int tens = (n % 100) / 10; int units = (n % 10); if (thousand >= 1) { if (thousand == 1) roman += "M"; else if (thousand == 2) roman += "MM"; else roman += "MMM"; } if (hundred >= 0) { if (hundred == 0) roman += ""; else if (hundred == 1) roman += "C"; else if (hundred == 2) roman += "CC"; else if (hundred == 3) roman += "CCC"; else if (hundred == 4) roman += "CD"; else if (hundred == 5) roman += "D"; else if (hundred == 6) roman += "DC"; else if (hundred == 7) roman += "DCC"; else if (hundred == 8) roman += "DCCC"; else roman += "CM"; } if (tens >= 0) { if (tens == 0) roman += ""; else if (tens == 1) roman += "X"; else if (tens == 2) roman += "XX"; else if (tens == 3) roman += "XXX"; else if (tens == 4) roman += "XL"; else if (tens == 5) roman += "L"; else if (tens == 6) roman += "LX"; else if (tens == 7) roman += "LXX"; else if (tens == 8) roman += "LXXX"; else roman += "XC"; } if (units >= 0) { if (units == 0) roman += ""; else if (units == 1) roman += "I"; else if (units == 2) roman += "II"; else if (units == 3) roman += "III"; else if (units == 4) roman += "IV"; else if (units == 5) roman += "V"; else if (units == 6) roman += "VI"; else if (units == 7) roman += "VII"; else if (units == 8) roman += "VIII"; else roman += "IX"; } } else { roman = "Number cannot be converted as it exceeds over 3999"; } return roman;

std::back_inserter

可以使用std :: copy将3D数组复制到向量。

2 个答案: