2019-03-28-fibonacci number

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

解析

1
2
3
4
5
6
7
8
9

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

1
2
3
4
5
6
7

var fib = function(N) {
    let arr = [0, 1];
    for(let i = 2; i <= N; i++) {
        arr[i] = arr[i-1] + arr[i-2];
    }
    return arr[N]; 
}