package algs.factorial;import java.math.BigInteger;/*** Author: areful* Date: 2019/3/6* 計算 sum(n!), n=1,2, ... 20*/
public class NFactorial {public static void main(String[] args) {System.out.println(calcFactorial0(3));System.out.println(calcFactorial1(3));System.out.println(calcFactorial2(3));System.out.println(calcFactorial0(50));System.out.println(calcFactorial1(50));System.out.println(calcFactorial2(50));}private static long calcFactorial0(int n) {long sum = 0L;long l = 1L;for (int i = 1; i <= n; i++) {l *= i;sum += l;}return sum;}private static double calcFactorial1(int n) {double sum = 0L;double l = 1L;for (int i = 1; i <= n; i++) {l *= i;sum += l;}return sum;}private static BigInteger calcFactorial2(int n) {BigInteger sum = BigInteger.valueOf(0L);BigInteger l = BigInteger.valueOf(1L);for (int i = 1; i <= n; i++) {BigInteger mul = BigInteger.valueOf(i);l = l.multiply(mul);sum = sum.add(l);}return sum;}
}
運行結果：
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