編程題目:
49.求1+2!+3!+…+20!的和。
示例代碼:
package program.calculation.exercise49;
import java.util.Scanner;
/**
* 49.求1+2!+3!+...+20!的和。
*/
public class FactorialSum {
public static void main(String[] args) {
System.out.println("請輸入項數:");
@SuppressWarnings("resource")
Scanner scanner = new Scanner(System.in);
int n = scanner.nextInt();
System.out.println("第一種方式(循環):");
System.out.println(n+"項階乘之和爲:"+loopFactorialSum(n));
System.out.println("第二種方式(遞歸):");
System.out.println(n+"項階乘之和爲:"+recurFactorialSum(n));
}
//第一種方式:循環
private static int loopFactorialSum(int n) {
int sum = 0;
for (int i=1; i<=n; i++) {
int factorial = 1; //每項階乘
for (int j=1; j<=i; j++) {
factorial *= j;
}
sum += factorial;
}
return sum;
}
//第二種方式:遞歸
private static int recurFactorialSum(int n){
int sum = 0;
for(int i=1; i<=n; i++) {
sum += recurFactorial(i);
}
return sum;
}
//求每項階乘(遞歸)
private static int recurFactorial(int n){
if(1 == n || 2 == n){
return n;
}else{
return n*recurFactorial(n-1);
}
}
}