Question

int arr[6] = {1, 4, 20, 3, 10, 5};

for (int i = 0; i < N; i++) {
    for (int j = i; j < N; j++) { 
       //some stuff...
    } 
}

//Above code is iterating twice to array.

将数组转换为矢量后。我必须在向量中应用相同的逻辑。请指导我如何迭代std::vector。

Answer 1

It depends on how you want to operate on the elements of std::vector<int> and whether you need the index information. E.g., if you want to iterate over std::vector<int> v and want to change the elements, you could use

for( auto& val : v )
{
    val = 0;
}

If you do not change the elements, use

for( const auto& val : v )
{
    std::cout << val << std::endl;
}

If you need index information, use the index operator []

std::size_t size = v.size();

for( std::size_t i = 0; i < size; ++i )
{
    v[i] = i;
}

Now, if you (really?) want to use std::vector<int> to store your data but need to be fast in a specific loop, maybe you should prefer something like

int* data = v.data();
std::size_t size = v.size();

for( std::size_t i = 0; i < size; ++i, ++data )
{
    *data = i;
}

从数组转换后迭代到向量

1 个答案: