如何在 C++ 中以相反的顺序添加一个向量与另一个向量？

Question

There is a vector vector<int>v
I want to add another vector vector<int>temp in reverse order with this vector.

For example,

   v = {1, 5, 7} and

temp = {11, 9, 8}

I want to add temp in reverse order, that is {8, 9, 11} to vector v .

So that, v will be : v = {1, 5, 7, 8, 9, 11}

Here's how i did it :

int a[] = {1, 5, 7};
vector<int>v(a,a+3);
int b[] = {11, 9, 8};
vector<int>temp(b,b+3);

for(int i=temp.size()-1;i>=0;i--)
  v.push_back(temp[i]);

for(int i=0;i<v.size();i++)
  cout<<v[i]<<" ";
cout<<"\n";

Is there a built in function in STL or C++ to do this ? or do i have to do it manually ?

Answer 1

Use reverse iterators:

std::vector<int> temp(v.rbegin(), v.rend());

Or std::reverse_copy() :

std::reverse_copy(v.begin(), v.end(), std::back_inserter(temp));

Answer 2

Try the following

v.insert( v.end(), temp.rbegin(), temp.rend() );

Here is a demonstrative program

#include <iostream>
#include <vector>

int main()
{
    int a[] = { 1, 5, 7 };
    std::vector<int> v( a, a + 3 );
    int b[] = { 11, 9, 8 };
    std::vector<int> temp( b, b + 3 );

    v.insert( v.end(), temp.rbegin(), temp.rend() );

    for ( int x : v ) std::cout << x << ' ';
    std::cout << std::endl;

    return 0;
}

The program output is

1 5 7 8 9 11