java 实现阶乘 三种方法

用三种方法来实现n!实现使用BigDecimal类,因为用int最多正确算到12!,用long最多正确算到20!.废话不多说,直接上代码:

//第一种方法:

Java代码

1. 1.package Factorial;
2. 2.
3. 3.import java.math.BigDecimal;
4. 4.import java.util.Scanner;
5. 5.public class Factorial1 {
6. 6. public static BigDecimal factorial(int n){
7. 7. BigDecimal result = new BigDecimal(1);
8. 8. BigDecimal a;
9. 9. for(int i = 2; i <= n; i++){
10. 10. a = new BigDecimal(i);
11. 11. result = result.multiply(a);
12. 12. }
13. 13. return result;
14. 14. }
15. 15.
16. 16. public static void main(String[] arguments){
17. 17. Scanner sc = new Scanner(System.in);
18. 18. int a = sc.nextInt();
19. 19. System.out.println(a + "!=" + factorial(a));
20. 20. }
21. 21.
22. 22.}
23. package Factorial;
24. import java.math.BigDecimal;
25. import java.util.Scanner;
26. public class Factorial1 {
27. public static BigDecimal factorial(int n){
28. BigDecimal result = new BigDecimal(1);
29. BigDecimal a;
30. for(int i = 2; i <= n; i++){
31. a = new BigDecimal(i);
32. result = result.multiply(a);
33. }
34. return result;
35. }
36. public static void main(String[] arguments){
37. Scanner sc = new Scanner(System.in);
38. int a = sc.nextInt();
39. System.out.println(a + "!=" + factorial(a));
40. }
41. }

第二种方法:

Java代码

1. 1.//第二种方法
2. 2.package Factorial;
3. 3.
4. 4.import java.math.BigDecimal;
5. 5.import java.util.Scanner;
6. 6.public class Factorial3 {
7. 7. public static BigDecimal factorial(BigDecimal n){
8. 8. BigDecimal bd1 = new BigDecimal(1);
9. 9. BigDecimal bd2 = new BigDecimal(2);
10. 10. BigDecimal result = bd1;
11. 11. while(n.compareTo(bd1) > 0){
12. 12. result = result.multiply(n.multiply(n.subtract(bd1)));
13. 13. n = n.subtract(bd2);
14. 14. }
15. 15. return result;
16. 16. }
17. 17. public static void main(String[] arguments){
18. 18. Scanner sc = new Scanner(System.in);
19. 19. BigDecimal n = sc.nextBigDecimal();
20. 20.
21. 21. System.out.print(n + "!=" + factorial(n));
22. 22. }
23. 23.
24. 24.}

//第二种方法

1. package Factorial;
2. import java.math.BigDecimal;
3. import java.util.Scanner;
4. public class Factorial3 {
5. public static BigDecimal factorial(BigDecimal n){
6. BigDecimal bd1 = new BigDecimal(1);
7. BigDecimal bd2 = new BigDecimal(2);
8. BigDecimal result = bd1;
9. while(n.compareTo(bd1) > 0){
10. result = result.multiply(n.multiply(n.subtract(bd1)));
11. n = n.subtract(bd2);
12. }
13. return result;
14. }
15. public static void main(String[] arguments){
16. Scanner sc = new Scanner(System.in);
17. BigDecimal n = sc.nextBigDecimal();
18. System.out.print(n + "!=" + factorial(n));
19. }
20. }

第三种方法,用递归实现:

Java代码

1. 1.package Factorial;
2. 2.
3. 3.import java.util.Scanner;
4. 4.import java.math.BigDecimal;
5. 5.public class Factorial2 {
6. 6. public static BigDecimal factorial(BigDecimal n){
7. 7. BigDecimal bd1 = new BigDecimal(1);
8. 8. if(n.equals(new BigDecimal(1))){
9. 9. return bd1;
10. 10. }
11. 11. else
12. 12. return n.multiply(factorial(n.subtract(bd1)));
13. 13. }
14. 14. public static void main(String[] arguments){
15. 15. Scanner sc = new Scanner(System.in);
16. 16. BigDecimal a = sc.nextBigDecimal();
17. 17. BigDecimal result = factorial(a);
18. 18. System.out.println(a + "!=" +result);
19. 19.
20. 20. }
21. 21.
22. 22.}