剑指offer 面试题9 斐波那契数列 java版答案

package OfferAnswer;
/**
* 面试题09
* 斐波那契数列
* @author lwk
*
*/
public class Answer09 {
public static void main(String[] args) {
long start = System.currentTimeMillis();
System.out.println(Fibonacci1(40));
long end = System.currentTimeMillis();
System.out.println(end - start);
}
//递归解法 时间复杂度指数递增
public static long Fibonacci1(int n){
if(n == 0){
return 0;
}
if(n == 1){
return 1;
}
return Fibonacci1(n-1) + Fibonacci1(n-2);
}

//时间复杂度O(n)的解法
public static long Fibonacci2(int n){
if(n == 0){
return 0;
}
if(n == 1){
return 1;
}
long first = 0;
long second = 1;
long result = 0;
for (int i = 2; i <= n; i++) {
result = first + second;
first = second;
second = result;
}
return result;
}
}