In mathematics, Fibonacci numbers are special integer sequences where a number is composed from summation of the past two numbers, as shown in the following the expression:
If we implement this using PHP 7, it will look like this:
function fibonacci(int $n): int {
if ($n == 0) {
return 1;
} else if ($n == 1) {
return 1;
} else {
return fibonacci($n - 1) + fibonacci($n - 2);
}
}
If we consider the preceding implementation, we can see it is a bit different from the previous examples. Now, we are calling two functions from one function call. We will discuss different types of recursions shortly.