LeetCode #509 Fibonacci Number Solution & Explanation

public class Solution {
    public int Fib(int n) {
        int first  = 0;     
        int second = 1;     
        int tmp = 0;        
        
        if(n<2)   
        {
            return n;
        }
        else
        {
            for(int i =2; i<=n;i++) 
            {
                tmp = second;       
                second+=first;     
                first = tmp;        
            }
        }
        return second;
    }
}

public class Solution {
    public int Fib(int n) {
        int[] arr = new int[31];
        arr[0] = 0;
        arr[1] = 1;
        
        for(int i = 2; i<=n; i++)
        {
            arr[i] = arr[i-1]+arr[i-2];
        }
        return arr[n];
    }
}

class Solution {
    public int fib(int n) {
        int[]arr = new int[31];

        arr[0] = 0;
        arr[1] = 1;
        
        for(int i = 2; i<=n; i++)
        {
            arr[i] = arr[i-1]+arr[i-2];
        }
        return arr[n];
    }
}

class Solution:
    def fib(self, n: int) -> int:
        arr = [0,1]
        
        for i in range(2,n+1):
            arr.append(arr[i-1]+arr[i-2])
        
        return arr[n]

/**
 * @param {number} n
 * @return {number}
 */
var fib = function(n) {
    arr = [0,1];
    
    for(let i = 2; i<=n; i++)
    {
        arr[i] = arr[i-1]+arr[i-2];
        //arr.push(arr[i-1]+arr[i-2])  //you can choose which one to use
    }
    return arr[n];
};