求斐波那契数列第n个数的效率比较

https://www.bilibili.com/video/BV1sX4y1G7oM?p=5&spm_id_from=pageDriver

?

1	求斐波那契数列第n个数

?

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53

package testpack;   /**  * 求斐波那契数列第n个数  */ public class T1 {     public static void main(String[] args) { //        System.out.println(fun1(60)); //        System.out.println(fun2(60));           int n = 76; //        TimeTool.check("fun1", new TimeTool.Task() { //            @Override //            public void execute() { //                System.out.println(fun1(n));//递归 //            } //        });           TimeTool.check("fun2", new TimeTool.Task() {             @Override             public void execute() {                 System.out.println(fun2(n));//循环             }         });     }       /**      * 递归实现      * @param n      * @return      */     public static long fun1(long n) {         if (n <= 1) return n;         return fun1(n - 1) + fun1(n - 2);     }       /**      * 循环实现      * @param n      * @return      */     public static int fun2(int n) {         if (n <= 1) return n;         int first = 0;         int second = 1;         for (int i = 0; i < n - 1; i++) {             int sum = first + second;             first = second;             second = sum;         }         return second;     } }

　　

?

1

计时器类

?

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

package testpack;   import java.text.SimpleDateFormat; import java.util.Date;   /**  * 计时器  */ public class TimeTool {     private static final SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss.SSS");       public interface Task {         void execute();     }       public static void check(String title, Task task) {         if (task == null) {             return;         }         title = (title == null) ? "" : ("[" + title + "]");         System.out.println(title);         System.out.println("开始：" + sdf.format(new Date()));         long begin = System.currentTimeMillis();         task.execute();         long end = System.currentTimeMillis();         System.out.println("结束：" + sdf.format(new Date()));         double time = (end - begin) / 1000.0;         System.out.println("耗时：" + time + "秒");         System.out.println("-------------------");     } }