Memoizing Fibonacci

// This is the canonical recursive definition of the Fibonacci function
int fib(int n)
{
    // First check the base case, the sequence always starts 0, 1
    if(n < 2) return n;
    return fib(n-1) + fib(n-2);
}

// Here's a memoized version
std::map<int, int> fib_memo;
int fib(int n)
{
    // First check the base case, the sequence always starts 0, 1
    if(n < 2) return n;
    // Then check to see if we've evaluated this one before -- if so, use that
    if(fib_memo.count(n)) return fib_memo[n];
    // Otherwise, calculate the value and store it before returning it
    int value = fib(n-1) + fib(n-2);
    fib_memo[n] = value;
    return value;
}