LOJ P10012 Best Cow Fences 题解

每日一题 day48 打卡

Analysis

二分答案，判断序列的平均值是否大于等于mid

具体怎么实现呢？

将序列减去mid，再用前缀和来维护平均值就好了

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define int long long
#define maxn 100000+10
#define INF 2147483647
#define rep(i,s,e) for(register int i=s;i<=e;++i)
#define dwn(i,s,e) for(register int i=s;i>=e;--i)
using namespace std;
inline int read()
{
    int x=0,f=1;
    char c=getchar();
    while(c<'0'||c>'9') {if(c=='-') f=-1; c=getchar();}
    while(c>='0'&&c<='9') {x=x*10+c-'0'; c=getchar();}
    return f*x;
}
inline void write(int x)
{
    if(x<0) {putchar('-'); x=-x;}
    if(x>9) write(x/10);
    putchar(x%10+'0');
}

int n,L,l,r,ans;
int a[maxn],sum[maxn],b[maxn];
inline bool check(int x)
{
    rep(i,1,n) b[i]=a[i];
    rep(i,1,n) b[i]-=x;
    rep(i,1,n) sum[i]=sum[i-1]+b[i];
    int min_val=INF;
    rep(i,L,n)
    {
        min_val=min(min_val,sum[i-L]);
        if(sum[i]-min_val>=0) return true;
    }
    return false;
}
signed main()
{
    n=read();L=read();
    rep(i,1,n) 
    {
        a[i]=read(); 
        a[i]*=1000;
    }
    l=0,r=100000000;
    while(l<r)
    {
        int mid=(l+r+1)/2;
        if(check(mid)==true) 
        {
            ans=mid;
            l=mid;
        }
        else r=mid-1;
    }
    if(ans%10==9) write(ans+1);
    else write(ans);
    return 0;
}

请各位大佬斧正（反正我不认识斧正是什么意思）