一本通 1434：【例题2】Best Cow Fences

Best Cow Fences

二分答案 + 前缀和

个人认为题意没有表述清楚，本题要求的是满足题意的连续子序列（难度大大降低了有木有）。

本题的精度也是非常令人陶醉，请您自行体会吧！

#include <iostream>
#include <cstdio>
#include <algorithm>
using namespace std;
//Mystery_Sky
//
#define M 10000100
#define ex 1e-5
double l = 100000.0, r = -10000.0, mid;
int n, L;
double a[M], sum[M];
inline bool check(double ans)
{
	double sum1, sum2, maxx;
	sum1 = sum[L-1] - (L-1) * ans;
	for(int i = L; i <= n; i++) {
		sum2 = sum[i] - sum[i - L] - L * ans;
		sum1 = sum1 + a[i] - ans;
		sum1 = max(sum1, sum2);
		if(sum1 > -ex) return true;
	}
	return false;
}

int main() {
	scanf("%d%d", &n, &L);
	for(int i = 1; i <= n; i++) {
		scanf("%lf", &a[i]);
		sum[i] = sum[i-1] + a[i];
		l = min(l, a[i]), r = max(r, a[i]);
	}
	while(r - l > ex) {
		mid = (l + r)/2;
		if(check(mid)) l = mid;
		else r = mid;
	}
	int ans = (int)(r * 1000);
	printf("%d", ans);
	return 0;
}