面试题9:斐波那契数列

一. 题目

写一个函数,输入n,求斐波那契数列的第n项.

代码请到我的代码库中下载 Point2Offer

二. 代码

内含传统解法和优化后的解法.

package com;

import java.util.Scanner;

/**
 * 剑指offer: 斐波那契数列
 * 方法:最优递归,
 * 测试用例:功能测试(输入3,5,7)
 * 边界值测试(0,1,2)
 * 性能测试(输入较大的数字:40,50,100等)
 * @author dingding
 * Date:2017-6-15 16:00
 * Declaration: All Rights Reserved!
 */
public class Fibonacci {

    public static void main(String[] args) {
        test1();
        test2();
        test3();
        test4();
        test5();
    }

    //原始的方法
    private static long fibonacci_formal(int n){
        if (n==0) {
            return 0;
        }else if (n==1||n==2) {
            return 1;
        }else {
            return fibonacci_formal(n-1)+fibonacci_formal(n-2);
        }
    }

    //计算
    private static long fibonacci_n(int n){
        int[] result = {0,1};
        if (n<2) {
            return result[n];
        }
        long fibNMinusOne = 1;
        long fibNMinusTwo = 0;
        long fibN = 0;
        for (long i=2;i<=n;++i){
            fibN = fibNMinusOne+fibNMinusTwo;
            fibNMinusTwo=fibNMinusOne;        //先给小的赋值
            fibNMinusOne=fibN;
        }
        return fibN;
    }

    /*====================测试用例==========================*/
    private static void test(){
        System.out.println("输入N: ");
        Scanner fin = new Scanner(System.in);
        int N = fin.nextInt();
        System.out.println();
        long result = fibonacci_n(N);
        System.out.println("结果为: "+result);
        System.out.println("=========================");
    }

    //输入5
    private static void test1() {
        test();
    }

    //输入0
    private static void test2() {
        test();
    }

    //输入1
    private static void test3() {
        test();
    }
    //输入40
    private static void test4() {
        test();
    }
    //测试原始方法
    private static void test5(){
        System.out.println("测试原始方法(递归耗时): ");
        long result = fibonacci_formal(20);
        System.out.println("结果为: "+result);
    }

}

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有不妥当之处,麻烦告知:D