Copying from one dimensional vector vector

I have multiple 3 one dimensional vectors (vector<int> starts, vector<int> ends, vector<int> points). Each having specific number of elements.

I want to create a two dimensional vector vector<pair<int,int>>matrix in such a sequence :

1. from beginning of matrix to size of start first element of matrix is elements of vector<int> starts and second element is "-1"
2. Append now the elements of vector<int> ends to matrix such that first element of matrix is elements of vector<int> ends and second element is "-2"

3. Append now the elements of vector<int> points to matrix such that first element of matrix is elements of vector<int> points and second element is Index of points.

   Visual Representation :-

   Input:

   starts: {1, 2, 3} ends: {4, 5, 6} points: (7, 8, 9}

   Output:

   matrix: { {1, -1}, {2, -1}, {3, -1}, {4, -2}, {5, -2}, {6, -2}, {7, 0}, {8, 1}, {9, 2} }

Currently I am using a push_back with for-loop function which works perfectly fine but when the input size is big code is very slow.

Code I am using is as follows:

vector<pair<int,int>> fast_count_segments(
    vector<int> starts, 
    vector<int> ends, 
    vector<int> points) 
{
   int i = 0;
   vector<pair<int,int>>matrix;

   for(i; i<starts.size(); i++) {
       matrix.push_back(make_pair(starts[i],-1));
   }
   for(i; i<starts.size()+ends.size(); i++) {
       matrix.push_back(make_pair(ends[i-starts.size()],-2));
   }
   for(i; i<starts.size()+ends.size()+points.size(); i++) {
        matrix.push_back(make_pair(
            points[i-starts.size()-ends.size()],
            i-(starts.size()+ends.size())
        ));
   }
   return matrix;
}

Can you please help on how to fill the 2D vector quickly with these requirements without iterating through each element. I am using C++11. Thanks in Advance !!