BZOJ 4491: 我也不知道题目名字是什么 线段树+离线

code:

#include <string>
#include <cstring>
#include <cstdio>
#include <algorithm>
#define N 50003
#define lson now<<1
#define rson now<<1|1
#define inf 100000000
using namespace std;
void setIO(string s) {
    string in=s+".in";
    string out=s+".out";
    freopen(in.c_str(),"r",stdin);
    // freopen(out.c_str(),"w",stdout);
}
int n;
int sm[N];
int bg[N];
int pos[N];
int val[N];
int mx[N<<2];
int mn[N<<2];
int answer[N];
struct node {
    int x;
    int id;
    node(int x=0,int id=0):x(x),id(id){}
}a[N<<1];
struct data {
    int l,r,id;
    data(int l=0,int r=0,int id=0):l(l),r(r),id(id){}
}e[N];
bool cmp(node a,node b) {
    return a.x==b.x?a.id<b.id:a.x<b.x;
}
bool cmp_data(data a,data b) {
    return a.r<b.r;
}
void build(int l,int r,int now) {
    if(l==r) {
        mn[now]=inf;
        mx[now]=-inf;
        return;
    }
    int mid=(l+r)>>1;
    build(l,mid,lson);
    build(mid+1,r,rson);
}
void fix_mn(int l,int r,int now,int p,int v) {
    if(l==r) {
        mn[now]=v;
        return;
    }
    int mid=(l+r)>>1;
    if(p<=mid) {
        fix_mn(l,mid,lson,p,v);
    }
    else {
        fix_mn(mid+1,r,rson,p,v);
    }
    mn[now]=min(mn[lson],mn[rson]);
}
void fix_mx(int l,int r,int now,int p,int v) {
    if(l==r) {
        mx[now]=v;
        return;
    }
    int mid=(l+r)>>1;
    if(p<=mid) {
        fix_mx(l,mid,lson,p,v);
    }
    else {
        fix_mx(mid+1,r,rson,p,v);
    }
    mx[now]=max(mx[lson],mx[rson]);
}
int que_mn(int l,int r,int now,int L,int R) {
    if(l>=L&&r<=R) {
        return mn[now];
    }
    int mid=(l+r)>>1,re=inf;
    if(L<=mid) {
        re=min(re,que_mn(l,mid,lson,L,R));
    }
    if(R>mid) {
        re=min(re,que_mn(mid+1,r,rson,L,R));
    }
    return re;
}
int que_mx(int l,int r,int now,int L,int R) {
    if(l>=L&&r<=R) {
        return mx[now];
    }
    int mid=(l+r)>>1,re=-inf;
    if(L<=mid) {
        re=max(re,que_mx(l,mid,lson,L,R));
    }
    if(R>mid) {
        re=max(re,que_mx(mid+1,r,rson,L,R));
    }
    return re;
}
int main() {
    // setIO("input");
    int i,j,cnt=0;
    scanf("%d",&n);
    for(i=1;i<=n;++i) {
        scanf("%d",&val[i]);
    }
    pos[n]=sm[n]=bg[n]=n;
    for(i=n-1;i>=1;--i) {
        sm[i]=(val[i+1]<=val[i]?sm[i+1]:i);
        bg[i]=(val[i+1]>=val[i]?bg[i+1]:i);
        pos[i]=max(sm[i],bg[i]);
        a[++cnt]=node(i,0);
        a[++cnt]=node(pos[i],i);
    }
    sort(a+1,a+1+cnt,cmp);
    int q;
    scanf("%d",&q);
    for(i=1;i<=q;++i) {
        scanf("%d%d",&e[i].l,&e[i].r);
        e[i].id=i;
    }
    sort(e+1,e+1+q,cmp_data);
    build(1,n,1);
    for(i=j=1;i<=q;++i) {
        while(j<=cnt&&a[j].x<=e[i].r) {
            if(a[j].id) {
                fix_mn(1,n,1,a[j].id,inf);
                fix_mx(1,n,1,a[j].id,a[j].x-a[j].id+1);
            }
            else {
                fix_mn(1,n,1,a[j].x,a[j].x);
            }
            ++j;
        }
        answer[e[i].id]=max(e[i].r-que_mn(1,n,1,e[i].l,e[i].r)+1, que_mx(1,n,1,e[i].l,e[i].r));
    }
    for(i=1;i<=q;++i) {
        printf("%d\n",answer[i]);
    }
    return 0;
}