509. Fibonacci Number

Easy

題目描述

Description

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.

Constraints:

0 <= n <= 30

解答

Solution

JavaScript

/**
 * @param {number} n
 * @return {number}
 */
var fib = function (n) {
  if (n === 0) {
    return 0;
  } else if (n === 1) {
    return 1;
  } else {
    return fib(n - 1) + fib(n - 2);
  }
};

解題思路

經典的 Fibonacci 數列題目，練習的是遞迴解法，除了 0 和 1 以外都是 fib(n - 1) + fib(n - 2) ，滿足遞迴自己呼叫自己的定義。

心得

超級經典題，而因為 Constraints: 0 <= n <= 30 最大只到30的關係，所以 Discussion 有個人寫了下面這段

I'm just gonna drop this right here...

int[] ans = 
{0,1,1,2,3,5,8,13,21,34,55,89,144,
233,377,610,987,1597,2584,4181,
6765,10946,17711,28657,46368,
75025,121393,196418,317811,514229,832040};

Go ahead, nobody is watching😈