​​http://codeforces.com/problemset/problem/193/D​​

和一道蓝桥题一个套路

 

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N=0x3f3f3f3f;
const int maxn=3e5+10;

struct node
{
    int minn1,minn2,cnt1,cnt2,laz;
};

node tree[4*maxn];
int ary[maxn],pos[maxn];
int n;

void change(int cur,int val)
{
    tree[cur].minn1+=val;
    if(tree[cur].minn2!=N) tree[cur].minn2+=val;
    tree[cur].laz+=val;
}

void pushup(int cur)
{
    tree[cur].minn1=min(tree[2*cur].minn1,tree[2*cur+1].minn1);
    tree[cur].minn2=N;
    if(tree[cur].minn1!=tree[2*cur].minn1) tree[cur].minn2=min(tree[cur].minn2,tree[2*cur].minn1);
    if(tree[cur].minn1!=tree[2*cur+1].minn1) tree[cur].minn2=min(tree[cur].minn2,tree[2*cur+1].minn1);
    tree[cur].minn2=min(tree[cur].minn2,min(tree[2*cur].minn2,tree[2*cur+1].minn2));
    tree[cur].cnt1=0;
    if(tree[cur].minn1==tree[2*cur].minn1) tree[cur].cnt1+=tree[2*cur].cnt1;
    if(tree[cur].minn1==tree[2*cur+1].minn1) tree[cur].cnt1+=tree[2*cur+1].cnt1;
    tree[cur].cnt2=0;
    if(tree[cur].minn2==tree[2*cur].minn1) tree[cur].cnt2+=tree[2*cur].cnt1;
    if(tree[cur].minn2==tree[2*cur+1].minn1) tree[cur].cnt2+=tree[2*cur+1].cnt1;
    if(tree[cur].minn2==tree[2*cur].minn2) tree[cur].cnt2+=tree[2*cur].cnt2;
    if(tree[cur].minn2==tree[2*cur+1].minn2) tree[cur].cnt2+=tree[2*cur+1].cnt2;
}

void pushdown(int cur)
{
    if(tree[cur].laz!=0){
        change(2*cur,tree[cur].laz);
        change(2*cur+1,tree[cur].laz);
        tree[cur].laz=0;
    }
}

void build(int l,int r,int cur)
{
    int m;
    tree[cur].minn1=0,tree[cur].minn2=N;
    tree[cur].cnt1=r-l+1,tree[cur].cnt2=0;
    tree[cur].laz=0;
    if(l==r) return;
    m=(l+r)/2;
    build(l,m,2*cur);
    build(m+1,r,2*cur+1);
    pushup(cur);
}

void update(int pl,int pr,int val,int l,int r,int cur)
{
    int m;
    if(pl<=l&&r<=pr){
        change(cur,val);
        return;
    }
    pushdown(cur);
    m=(l+r)/2;
    if(pl<=m) update(pl,pr,val,l,m,2*cur);
    if(pr>m) update(pl,pr,val,m+1,r,2*cur+1);
    pushup(cur);
}

ll query(int pl,int pr,int l,int r,int cur)
{
    ll res;
    int m;
    if(pl<=l&&r<=pr){
        res=0;
        if(tree[cur].minn1==1||tree[cur].minn1==2) res+=(ll)(tree[cur].cnt1);
        if(tree[cur].minn2==1||tree[cur].minn2==2) res+=(ll)(tree[cur].cnt2);
        return res;
    }
    pushdown(cur);
    res=0,m=(l+r)/2;
    if(pl<=m) res+=query(pl,pr,l,m,2*cur);
    if(pr>m) res+=query(pl,pr,m+1,r,2*cur+1);
    return res;
}

int main()
{
    ll ans;
    int i,tmp,x,y;
    scanf("%d",&n);
    for(i=1;i<=n;i++){
        scanf("%d",&tmp);
        pos[tmp]=i;
    }
    build(1,n,1);
    ans=0;
    for(i=n;i>=1;i--){
        ary[pos[i]]=i;
        x=ary[pos[i]-1],y=ary[pos[i]+1];
        if(x>y) swap(x,y);
        if(x==0&&y==0){
            //printf("#1 %d %d %d\n",i,n,1);
            update(i,n,1,1,n,1);
        }
        else if(x==0&&y!=0){
            //printf("#2 %d %d %d\n",i,y-1,1);
            update(i,y-1,1,1,n,1);
        }
        else{
            //printf("#3 %d %d %d\n",i,x-1,1);
            //printf("#3 %d %d %d\n",y,n,-1);
            update(i,x-1,1,1,n,1);
            update(y,n,-1,1,n,1);
        }
        ans+=query(i,n,1,n,1);
        //printf("***%d %lld***\n",i,ans);
    }
    printf("%lld\n",ans-n);
    return 0;
}