Recursion
1.从前有个⼭山， 2.⼭山⾥里里有个庙， 3.庙⾥里里有个和尚讲故事:
计算 n!
n！= 1*2*3*...*n
function Factorial(n) {
if (n <= 1) return 1;
return n * Factorial(n - 1);
}
// Fibonacci array: 1, 1, 2, 3, 5, 13, 21, 34, ...
// F(n) = F(n-1) + F(n-2)
function fib(n) {
if (n == 0 || n == 1) return n
return fib(n - 1) + fib(n - 2)
}