19_08_26校内训练[Max]

题意

求$max_{l \leq r}{\{min{\{a_l,a_{l+1},...,a_r\}}*(r-l+1)\}}$

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思考

分治，考虑一个区间跨过某个点的贡献即可。

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代码

 #include<bits/stdc++.h>
 using namespace std;
 typedef long long int ll;
 const int maxn=5E5+;
 const int inf=1E9;
 int n;
 ll ans,a[maxn];
 inline ll max(ll x,ll y)
 {
     return x>y?x:y;
 }
 inline ll min(ll x,ll y)
 {
     return x<y?x:y;
 }
 void solve(int l,int r)
 {
     if(l==r)
     {
         ans=max(ans,a[l]);
         return;
     }
     int mid=(l+r)>>;
     ll nowL=a[mid],nowR=a[mid+];
     for(int i=mid+,j=mid;i<=r;++i,nowR=min(nowR,a[i]))
     {
         while(j>=l&&nowL>=nowR)
         {
             --j;
             nowL=min(nowL,a[j]);
         }
         ll len=i-j;
         ans=max(ans,len*nowR);
     }
     nowL=a[mid],nowR=a[mid+];
     for(int i=mid,j=mid+;i>=l;--i,nowL=min(nowL,a[i]))
     {
         while(j<=r&&nowL<=nowR)
         {
             ++j;
             nowR=min(nowR,a[j]);
         }
         ll len=j-i;
         ans=max(ans,len*nowL);
     }
     solve(l,mid),solve(mid+,r);
 }
 int main()
 {
     ios::sync_with_stdio(false);
     cin>>n;
     for(int i=;i<=n;++i)
         cin>>a[i];
     solve(,n);
     cout<<ans<<endl;
     return ;
 }