Check if number is period of sequence in C-CodePudding

I need to check if number is a period of sequence.

EXAMPLE: { 1, 3, 1, 4, 2, 1, 3, 1, 4, 2, 1, 3 }

Periods are 5 and 10. Base period is 5 because it is the smallest period.

#include <iostream>
#include <vector>
int p=0;
int period(std::vector<double>v , int x)
{
    int p = 0;
    for (int i = 1; !p && i < v.size(); i  )
    {
        int j = 0;
        while (j < v.size() - i && v[j] == v[j   i])   j;
        if ( j   i == v.size() ) p = i;
    }
    if(p!=x)
    return false;
    return true;
}

int main()
{
    std::vector<double> v = { 1, 3, 1, 4, 2, 1, 3, 1, 4, 2, 1, 3 };
    std::cout << period( v,10 ) << '\n';
}

My code checks if number is equal to base period. How could I check if it is equal to any of the periods and in that case return true?

CodePudding user response：

The function can be defined the following way

bool period( const std::vector<double> &v , size_t n )
{
    bool is_period = false;

    if ( n < v.size() )
    {
        size_t j = 0;
        while ( j < v.size() - n && v[j] == v[j   n])   j;
        is_period = j   n == v.size();
    }

    return is_period;
}

Here is a demonstration program.

#include <iostream>
#include <vector>

bool period( const std::vector<double> &v, size_t n )
{
    bool is_period = false;

    if (n < v.size())
    {
        size_t j = 0;
        while (j < v.size() - n && v[j] == v[j   n])   j;
        is_period = j   n == v.size();
    }

    return is_period;
}

int main()
{
    std::vector<double> v = { 1, 3, 1, 4, 2, 1, 3, 1, 4, 2, 1, 3 };

    if (period( v, 5 )) std::cout << 5 << " is a period\n";
    if (period( v, 10 )) std::cout << 10 << " is a period\n";
}

The program output is

5 is a period
10 is a period

CodePudding user response：

You could try checking your answer in rotations of modulo(%) period, as in the smallest period, which in this case is 5.