CSP认证（2022-06-12）

The more people you love, the weaker you are.
The things we love destroy us every time.

\(vscode\)也配置好了，\(html\)慢慢摸索着也能写些简单的本地网页了，\(CSP\)报名了，等一个小时后的两点\(N2\)也可以报名了。一切都刚刚开始，一切的一起，从结束中。太阳底下没有新鲜事，每次日出都是盛大开场
假面的小丑，上台了，不管他愿不愿意，只是履行着久远岁月最初的约定
尽管只剩他一个人记得约定
尽管步履蹒跚，跌跌撞撞
男人，就是为了一个遥远的约定不惜代价，浪漫至死的笨蛋

It's a trick, a shadow on the wall. And a very small man can cast a very large shadow.

• 归一化处理

AC代码

# include "bits/stdc++.h"
using namespace std;
int main() {
	int n;
	scanf("%d", &n);
	vector<double> a(n + 1);
	double sum = 0;
	for(int i = 1; i <= n; ++i) scanf("%lf", &a[i]), sum += a[i];
	double ave = sum / (double) n;
	sum = 0;
	for(int i = 1; i <= n; ++i) sum += (a[i] - ave) * (a[i] - ave);
	double dev = sqrt(sum / (double) n);
	for(int i = 1; i <= n; ++i) printf("%.16lf\n", (a[i] - ave) / dev);
	return 0;
}

然而，比$AC$代码更有价值的是

60分（精度问题）代码

# include "bits/stdc++.h"
using namespace std;
double a[1003];
int main() {
freopen("in.txt", "r", stdin);
	int n;
	scanf("%d", &n);
//	vector<long double> a(n + 1); 
	for(int i = 1; i <= n; ++i) {
		scanf("%lf", &a[i]);
	}
//	if(n == 1) {
//		printf("0");
//		return 0;
//	}
	double ave = accumulate(a + 1, a + n + 1, 0) / (double) (1.0 * n);
	double sum = accumulate(a + 1, a + n + 1, 0, [ave](double sum, double val) {
		return sum + (ave - val) * (ave - val);
	});
	
	double dev = sqrt(sum / (double) (1.0 * n));

	auto calc = [&](double x) {
		return (x - ave) / dev;
	};
	for(int i = 1; i <= n; ++i) {
		printf("%.16lf\n", calc(a[i]));
	}
	return 0;
}

同样的思路，简单的过程，却在精度上产生了截然不同的效果。 至少，我认识了$accumulate$的危险，就不会为了炫技而使用它了