LC509-Fibonacci-Number.java

/*
The Fibonacci numbers, commonly denoted F(n) form a sequence,
called the Fibonacci sequence, such that each number is the sum
of the two preceding ones, starting from 0 and 1. That is,

F(0) = 0, F(1) = 1
F(n) = F(n - 1) + F(n - 2), for n > 1.
Given n, calculate F(n).

Example 1:
Input: n = 2
Output: 1
Explanation: F(2) = F(1) + F(0) = 1 + 0 = 1.

Example 2:
Input: n = 3
Output: 2
Explanation: F(3) = F(2) + F(1) = 1 + 1 = 2.

Example 3:
Input: n = 4
Output: 3
Explanation: F(4) = F(3) + F(2) = 2 + 1 = 3.


Constraints:
0 <= n <= 30
*/

class Solution {
    public int fib(int n) {
        if (n == 0){
            return 0;
        }
        int prev = 0;
        int cur = 1;
        int newNum;
        for (int i=2; i <= n; i++){
            newNum = prev + cur;
            prev = cur;
            cur = newNum;
        }
        return cur;
    }
}