POJ 2018 Best Cow Fences（二分最大区间平均数）题解

#include<set>
#include<map>
#include<stack>
#include<cmath>
#include<queue>
#include<vector>
#include<string>
#include<cstdio>
#include<cstring>
#include<sstream>
#include<iostream>
#include<algorithm>
typedef long long ll;
using namespace std;
const int maxn = 1e5 + 10;
const int MOD = 1e9 + 7;
const int INF = 0x3f3f3f3f;
double a[maxn], dis[maxn], sum[maxn];
int main(){
    int n, f;
    while(~scanf("%d%d", &n, &f)){
        for(int i = 1; i <= n; i++){
            scanf("%lf", &a[i]);
        }
        sum[0] = 0;
        double l = -2001, r = 2001, ans = -1;
        while(r - l > 1e-6){
            double m = (l + r) / 2.0;
            for(int i = 1; i <= n; i++){
                dis[i] = a[i] - m;
                sum[i] = sum[i - 1] + dis[i];
            }
            double tmp = -INF, left = INF;
            for(int i = f, j = 0; i <= n; i++, j++){
                left = min(left, sum[j]);
                tmp = max(tmp, sum[i] - left);
            }
            if(tmp > 0){
                l = m;
            }
            else{
                r = m;
            }
            ans = m;
        }
        printf("%d\n", (int)(1000 * r));
    }
    return 0;
}