366. Fibonacci

描述

查找斐波纳契数列中第 N 个数.

所谓的斐波纳契数列是指：

• 前2个数是 0 和 1 。
• 第 i 个数是第 i-1 个数和第i-2 个数的和。
  
  斐波纳契数列的前10个数字是：

0, 1, 1, 2, 3, 5, 8, 13, 21, 34 ...

public class Solution {
    /**
     * @param n: an integer
     * @return: an ineger f(n)
     */
    public int fibonacci(int n) {
        // write your code here
        if (n == 1){
            return 0;
        } 

      	int[] arr = new int[n];
    	arr[0] = 0;
    	arr[1] = 1;
    	for(int i=2;i<n;i++) {
    		arr[i] = arr[i-1] + arr[i-2];

    	}
    	return arr[n-1];
    }
}

Error：递归实现斐波拉契数列超时

class Solution {
    /**
     * @param n: an integer
     * @return: an ineger f(n)
     */
    public int fibonacci(int n) {
        // write your code here
        if (n == 1){
            return 0;
        }else if(n == 2){
            return 1;
        }

        return fibonacci(n-1) + fibonacci(n-2);
    }
}

Description
Find the Nth number in Fibonacci sequence.

A Fibonacci sequence is defined as follow:

The first two numbers are 0 and 1.
The i th number is the sum of i-1 th number and i-2 th number.
The first ten numbers in Fibonacci sequence is:

0, 1, 1, 2, 3, 5, 8, 13, 21, 34 ...