Test2.java(java homework)

1   設n為自然數，編程計算∑n!的值；

import java.util.*;<br />public class Main {<br />public static void main(String[] args) {<br />Scanner in = new Scanner(System.in);<br />System.out.println("Input n:");<br />int n, result = 1, ans = 0;;<br />n = in.nextInt();<br />for (int i = 1; i <= n; ++i) {<br />result = 1;<br />for (int j = 1; j <= i; ++j) {<br />result *= j;<br />}<br />ans += result;<br />}<br />System.out.println("n! = " + ans);<br />}<br />}

//這個O(n^2)比較土；

 

import java.util.*;<br />public class Main {<br />public static void main(String[] agrs) {<br />Scanner in= new Scanner(System.in);<br />System.out.println("Input n:");<br />int n = in.nextInt();<br />int result = 1, ans = 0;<br />for(int i=1; i<=n; ++i) {<br />result *= i;<br />ans += result;<br />}<br />System.out.println(ans);<br />}<br />}

//這個O（n）主要是儲存中間變數的思想要掌握！