Question

I’m making a tic tac toe game and I’m making the player’s opponent now. As you know a tic tac toe match has 9 fields, so I’ve made a vector that contains all the fields that are already used by other X’s and O’s.

std::vector<int> UsedPositions;

So before I tried getting a random value with srand(time()) and iterate through the vector to check if that position was already being used. It actually worked but it took, as you can imagine, a lot of calculations (thus time) for my poor CPU because if the vector had about 8 elements it would mean it would have to iterate 8 times (that is IF the random number is distinct, else it would have to go through it another 8 times).

TL;DR – How do I get a distinct random value that is < 10 && > 0 from a vector?

Code thats slow for me:

int FindUniqueAnswer()
{
    int answer;
    bool AnswerFound = false;

    while(!AnswerFound)
    {
        bool DoesntEqual = true;
        srand(time(0));
        int random = rand()%10;
        if(random == 0)
        {
            random++;
        }

        for(int i = 0;i<UsedPositions.size();i++)
        {
            if(random == UsedPositions.at(i))
            {
                DoesntEqual = false;
                break;
            }
        }
        if(DoesntEqual)
        {
            answer = random;
            AnswerFound = true;
        }
    }

    return answer;
}

Answer 1

#include <random>
#include <algorithm>
...
vector<int> v = {1, 2, 3, 4, 5, 6, 7, 8, 9};
std::random_device rd
mt19937 g(rd());
shuffle(v.begin(), v.end(), g);

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