洛谷P3246 [HNOI2016]序列

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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[1<<21],*p1=buf,*p2=buf;
int read(){
    #define num ch-'0'
    char ch;bool flag=0;int res;
    while(!isdigit(ch=getc()))
    (ch=='-')&&(flag=true);
    for(res=num;isdigit(ch=getc());res=res*10+num);
    (flag)&&(res=-res);
    #undef num
    return res;
}
char sr[1<<21],z[20];int C=-1,Z;
inline void Ot(){fwrite(sr,1,C+1,stdout),C=-1;}
void print(ll x){
    if(C>1<<20)Ot();if(x<0)sr[++C]=45,x=-x;
    while(z[++Z]=x%10+48,x/=10);
    while(sr[++C]=z[Z],--Z);sr[++C]='\n';
}
const int N=1e5+5,inf=0x3f3f3f3f;
int n,m,top,bin[17],f[N][17],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+1];return cmp(f[l][k],f[r-bin[k]+1][k]);}
int main(){
//    freopen("testdata.in","r",stdin);
    n=read(),m=read(),a[n+1]=a[0]=inf;
    bin[0]=1;for(int i=1;i<=16;++i) bin[i]=bin[i-1]<<1;
    for(int i=2;i<=n;++i) log[i]=log[i>>1]+1;
    for(int i=1;i<=n;++i) a[i]=read(),f[i][0]=i;
    for(int j=1;j<=log[n];++j) for(int i=1;i<=n-bin[j-1]+1;++i)
    f[i][j]=cmp(f[i][j-1],f[i+bin[j-1]][j-1]);
    for(int i=1;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-1],suf[s[top--]]=n+1;
    for(int i=1;i<=n;++i) fr[i]=(ll)a[i]*(i-Pre[i])+fr[Pre[i]],gr[i]=gr[i-1]+fr[i];
    for(int i=n;i;--i) fl[i]=(ll)a[i]*(suf[i]-i)+fl[suf[i]],gl[i]=gl[i+1]+fl[i];
    while(m--){
        int l=read(),r=read(),p=query(l,r);
        print((ll)(p-l+1)*(r-p+1)*a[p]+
            gr[r]-gr[p]-fr[p]*(r-p)+
            gl[l]-gl[p]-fl[p]*(p-l));
    }
    return Ot(),0;
}