C++ - Fastest way to add an item to a sorted array

Question

I\'ve got a database with approximately 200 000 items, which is sorted by username. Now when I add an item to end of array and call my quick sort function to sort that array it

Answer 1

int add(Container c, int r, int l, Unit t)
{
    if(c[r]>t)
        return r;
    if(c[l]<t)
        return l+1;
    if(c[r]==c[l])
    {
         if(c[r]==t)
            return -1;
         return -1;
    }
    int m=(r+l)/2;
    if(c[m]==t)
          return -1;
    if(c[m]>t)
          return add(c,m,l,t);
    if(c[m]<t)
          return add(c,r,m,t);
}

It will probably give you the index you need to add...I hope it can help.It assumes you do not need to add when its already in.

Answer 2

Reinventing the wheel is fine if you want to learn how to code binary search, otherwise reusing is better.

std::lower_bound performs a binary search on a sorted range [first, last), returning an iterator to the searched element x if already present; otherwise the iterator would be pointing to the first element greater than x. Since standard containers' exposing an insert would insert before the iterator, this iterator can be used as-is. Here's a simple example.

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

int main()
{
    std::list<int> data = { 1, 5, 7, 8, 12, 34, 52 };

    auto loc = std::lower_bound(data.begin(), data.end(), 10);
    // you may insert 10 here using loc
    std::cout << *loc << '\n';

    loc = std::lower_bound(data.begin(), data.end(), 12);
    // you may skip inserting 12 since it is in the list (OR)
    // insert it if you need to; it'd go before the current 12
    std::cout << *loc << '\n';
}

12

12