0509. Fibonacci Number (E)

题目

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

题意

斐波那契数列生成。

思路

迭代或递归都很容易实现。

代码实现

Java

class Solution {
    public int fib(int n) {
        if (n == 0 || n == 1) return n;
        int a = 0, b = 1;
        for (int i = 2; i <= n; i++) {
            b = a + b;
            a = b - a;
        }
        return b;
    }
}