洛谷P3246 [HNOI2016]序列

传送门

题解

 //minamoto
 #include<iostream>
 #include<cstdio>
 #define ll long long
 using namespace std;
 #define getc() (p1==p2&&(p2=(p1=buf)+fread(buf,1,1<<21,stdin),p1==p2)?EOF:*p1++)
 char buf[<<],*p1=buf,*p2=buf;
 int read(){
     #define num ch-'0'
     char ch;bool flag=;int res;
     while(!isdigit(ch=getc()))
     (ch=='-')&&(flag=true);
     for(res=num;isdigit(ch=getc());res=res*+num);
     (flag)&&(res=-res);
     #undef num
     return res;
 }
 char sr[<<],z[];int C=-,Z;
 inline void Ot(){fwrite(sr,,C+,stdout),C=-;}
 void print(ll x){
     if(C><<)Ot();if(x<)sr[++C]=,x=-x;
     while(z[++Z]=x%+,x/=);
     while(sr[++C]=z[Z],--Z);sr[++C]='\n';
 }
 const int N=1e5+,inf=0x3f3f3f3f;
 int n,m,top,bin[],f[N][],a[N],Pre[N],suf[N],s[N],log[N];ll fl[N],fr[N],gl[N],gr[N];
 inline int cmp(int x,int y){return a[x]<a[y]?x:y;}
 inline int query(int l,int r){int k=log[r-l+];return cmp(f[l][k],f[r-bin[k]+][k]);}
 int main(){
 //    freopen("testdata.in","r",stdin);
     n=read(),m=read(),a[n+]=a[]=inf;
     bin[]=;for(int i=;i<=;++i) bin[i]=bin[i-]<<;
     for(int i=;i<=n;++i) log[i]=log[i>>]+;
     for(int i=;i<=n;++i) a[i]=read(),f[i][]=i;
     for(int j=;j<=log[n];++j) for(int i=;i<=n-bin[j-]+;++i)
     f[i][j]=cmp(f[i][j-],f[i+bin[j-]][j-]);
     for(int i=;i<=n;++i){
         while(top&&a[s[top]]>a[i]) suf[s[top--]]=i;
         Pre[i]=s[top],s[++top]=i;
     }while(top) Pre[s[top]]=s[top-],suf[s[top--]]=n+;
     for(int i=;i<=n;++i) fr[i]=(ll)a[i]*(i-Pre[i])+fr[Pre[i]],gr[i]=gr[i-]+fr[i];
     for(int i=n;i;--i) fl[i]=(ll)a[i]*(suf[i]-i)+fl[suf[i]],gl[i]=gl[i+]+fl[i];
     while(m--){
         int l=read(),r=read(),p=query(l,r);
         print((ll)(p-l+)*(r-p+)*a[p]+
             gr[r]-gr[p]-fr[p]*(r-p)+
             gl[l]-gl[p]-fl[p]*(p-l));
     }
     return Ot(),;
 }