[Leetcode] 509. Fibonacci Number

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.

 

난이도: easy 

DP

var fib = function(n) {
    const arr = new Array(n).fill(0);
    arr[0] = 0;
    arr[1] = 1;
    arr[2] = 1;
    
    for (let i = 3; i < n + 1; i++) {
        arr[i] = arr[i - 1] + arr[i - 2];
    }
    
    return arr[n]
};

 

 

Recursive

var fib = function(n) {
    if (n === 0) return 0;
    if (n === 1) return 1;
    
    return fib(n - 1) + fib(n - 2);
}

 

물론 효율은 DP로 풀이하는 것이 훨씬 좋다