LeetCode

Fibonacci_Number.swift

class Solution {
    
    func fib(_ N: Int) -> Int {
        
        return self.recursiveWay(N)
        
    }
    
    func recursiveWay(_ N: Int) -> Int {
        if N == 0 { return 0 }
        if N == 1 { return 1 }
        
        var memo = [Int](repeating: 0, count: 3)
        memo[0] = 0
        memo[1] = 1
        
        for _ in 2...N {
            memo[2] = memo[1] + memo[0]
            memo[0] = memo[1]
            memo[1] = memo[2]
        }
        
        return memo[2]
    }
    
    func iterationWay(_ N: Int) -> Int {
        if N == 0 { return 0 }
        if N == 1 { return 1 }
        
        return self.iterationWay(N-1) + self.iterationWay(N-2)
    }
}