实现 1！+ 2！+ 3！+ ... + n!

#include<iostream>
using namespace std;

//阶乘和 最优
int fSum(int N){
	int cur = 1;
	int ans = 0;
	for (int i = 1; i <= N; i++){
		cur *= i;// 1*1 1*2 2*3 6*4
		ans += cur;
	}
	return ans;
}

int main01(){
	cout << fSum(5) << endl;//1!+2!+3!+4!=1+2+6+24+120=
	system("pause");
	return 0;
}