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

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

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

/*
 * 509. Fibonacci Number
 * https://leetcode.com/problems/fibonacci-number/submissions/
 * https://realneo.me/509-fibonacci-number/submissions/
 */

public class Fib {
    public static void main(String[] args) {
        Fib solution = new Fib();

        System.out.println(solution.fib(5));
        System.out.println(solution.fib(20));
    }

    private int fib(int N) {
        if (N == 0) return 0;
        if (N == 1) return 1;

        int[] fib = new int[N + 1];
        fib[0] = 0;fib[1] = 1;
        for (int i = 2; i <= N; i++)
            fib[i] = fib[i - 1] + fib[i - 2];

        return fib[N];
    }
}