ref

#include <algorithm>
#include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;
typedef long long ll;
int n, q, a[100005], l[100005], r[100005], sta[100005], din, blc, bel[100005], st[100005][19], mii[17], mlg[100005];
ll sl[100005], sr[100005], now, ans[100005];
struct Ques{
    int ll, rr, id;
}qu[100005
 
];
bool cmp(Ques x, Ques y){
    if(bel[x.ll]!=bel[y.ll])    return bel[x.ll]<bel[y.ll];
    if(bel[x.ll]&1) return x.rr<y.rr;
    return x.rr>y.rr;
}
int getPos(int x, int y){
    int l=mlg[y-x+1], k=y+1-mii[l];
    return a[st[x][l]]<a[st[k][l]]?st[x][l]:st[k][l];
}
ll calL(int x, int
 
 y){
    int p=getPos(x, y);
    return (ll)a[p]*(y-p+1)+sr[x]-sr[p];
}
ll calR(int x, int y){
    int p=getPos(x, y);
    return (ll)a[p]*(p-x+1)+sl[y]-sl[p];
}
int main(){//freopen("sequence9.in", "r", stdin);
    cin>>n>>q;
    blc = sqrt(n);
    for(int i=1; i<=n; i++){
        scanf("
 
%d", &a[i]);
        bel[i] = (i - 1) / blc + 1;
        st[i][0] = i;
    }
    for(int i=1; i<=q; i++){
        scanf("%d %d", &qu[i].ll, &qu[i].rr);
        qu[i].id = i;
    }
    sort(qu+1, qu+1+q, cmp);
    for(int i=1; i<=n; i++){
        while(din && a[sta[din]]>=a[i]) din--;
        if(din) l[i] = sta[din];
        sta[++din] = i;
    }
    din = 0;
    for(int i=n; i; i--){
        r[i] = n + 1;
        while(din && a[sta[din]]>=a[i]) din--;
        if(din) r[i] = sta[din];
        sta[++din] = i;
    }
    mii[0] = 1;
    for(int i=1; i<=16; i++)
        mii[i] = mii[i-1] << 1;
    for(int i=2; i<=n; i++)
        mlg[i] = mlg[i>>1] + 1;
    for(int j=1; j<=16; j++)
        for(int i=1; i<=n; i++){
            st[i][j] = st[i][j-1];
            int k=i+mii[j-1];
            if(k<=n)    st[i][j] = (a[st[i][j-1]]<a[st[k][j-1]])?st[i][j-1]:st[k][j-1];
        }
    for(int i=1; i<=n; i++)
        sl[i] = sl[l[i]] + (ll)(i - l[i]) * a[i];
    for(int i=n; i; i--)
        sr[i] = sr[r[i]] + (ll)(r[i] - i) * a[i];
    int gtl=qu[1].ll, zzh=gtl-1;
    for(int i=1; i<=q; i++){
        while(gtl>qu[i].ll) now += calL(--gtl, zzh);
        while(zzh<qu[i].rr) now += calR(gtl, ++zzh);
        while(gtl<qu[i].ll) now -= calL(gtl++, zzh);
        while(zzh>qu[i].rr) now -= calR(gtl, zzh--);
        ans[qu[i].id] = now;
    }
    for(int i=1; i<=q; i++)
        printf("%lld\n", ans[i]);
    return 0;
}

loj2051 「HNOI2016」序列