C++: Fastest method to check if all array elements are equal

Question

What is the fastest method to check if all elements of an array(preferable integer array) are equal. Till now I have been using the following code:

bool chec         


        

Answer 1

In theory, I would propose this:

bool check_single(const int a[], int n)
{
    for (int i = 1; i < n; ++i) {
        if (a[0] != a[n]) { return false; }
    }
    return true;
}

Compared to other (already proposed) versions:

• a[0] will be hoisted outside the loop by the compiler, meaning a single array access within the loop
• we loop from 0 to n, which is better (access-wise) than loading a[0] and then looping from a[n]

Obviously, it still checks N elements and thus is O(N).