Question:
Given a number n, give me a function that returns the nth fibonacci number. Running time, space complexity, iterative vs. recursive.
// Recusive
// O(2^n)
public int fibonacci(int n)
{
if (n <= 0)
return 0;
if (n == 1)
return 1;
if (n == 2)
return 2;
return fibonacci(n - 2) + fibonacci(n - 1);
}
// Iterative
// O(n)
public int fibonacci(int n)
{
if (n <= 0)
return 0;
if (n == 1)
return 1;
if (n == 2)
return 2;
// last, cur, next
int last = 1;
int cur = 2;
for (int i = 3 ; i <= n ; i ++)
{
int temp = cur;
cur = cur + last;
last = temp;
}
return cur;
}