学步园

~~

#include <iostream>
#include <cstring>
#include <cstdio>
#define lson pos<<1
#define rson pos<<1|1
using namespace std;
const int MAXN=100005;
struct node
{
    int l,r;
    int msum;
    int lsum,rsum;
    int mid()
    {
        return (l+r)>>1;
    }
};
node tree[MAXN*4];
int num[MAXN];
inline void pushup(int pos)
{
    tree[pos].msum=max(tree[lson].msum,tree[rson].msum);
    tree[pos].lsum=tree[lson].lsum;
    tree[pos].rsum=tree[rson].rsum;
    if(num[tree[lson].r]<num[tree[rson].l])
    {
        tree[pos].msum=max(tree[pos].msum,tree[lson].rsum+tree[rson].lsum);
        if(tree[lson].lsum==tree[lson].r-tree[lson].l+1)
            tree[pos].lsum+=tree[rson].lsum;
        if(tree[rson].rsum==tree[rson].r-tree[rson].l+1)
            tree[pos].rsum+=tree[lson].rsum;
    }
}
void build(int l,int r,int pos)
{
    tree[pos].l=l;
    tree[pos].r=r;
    if(l==r)
    {
        tree[pos].lsum=tree[pos].rsum=tree[pos].msum=1;
        return ;
    }
    int mid=tree[pos].mid();
    build(l,mid,lson);
    build(mid+1,r,rson);
    pushup(pos);
}
void update(int a,int b,int pos)
{
    if(tree[pos].l==tree[pos].r)
    {
        num[a]=b;
        return ;
    }
    int mid=tree[pos].mid();
    if(a<=mid)
        update(a,b,lson);
    else
        update(a,b,rson);
    pushup(pos);
}
int queryL(int l,int r,int pos)
{
    if(r-l+1>=tree[pos].lsum)
        return tree[pos].lsum;
    else
        return r-l+1;
}
int queryR(int l,int r,int pos)
{
    if(r-l+1>=tree[pos].rsum)
        return tree[pos].rsum;
    else
        return r-l+1;
}
int query(int l,int r,int pos)
{
    if(l==tree[pos].l&&r==tree[pos].r)
        return tree[pos].msum;
    int mid=tree[pos].mid();
    if(r<=mid)
        return query(l,r,lson);
    else if(l>mid)
        return query(l,r,rson);
    else
    {
        int res=0;
        if(num[tree[lson].r]<num[tree[rson].l])
            res=max(res,queryR(l,mid,lson)+queryL(mid+1,r,rson));
        res=max(res,query(l,mid,lson));
        res=max(res,query(mid+1,r,rson));
        return res;
    }
}

int main()
{
    int n,m,t;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d%d",&n,&m);
        int i;
        for(i=1;i<=n;i++)
            scanf("%d",&num[i]);
        build(1,n,1);
        char word[2];
        for(i=1;i<=m;i++)
        {
            int a,b;
            scanf("%s%d%d",word,&a,&b);
            if(word[0]=='U')
                update(a+1,b,1);
            else
            {
                int x=query(a+1,b+1,1);
                printf("%d\n",x);
            }
        }
    }

    return 0;
}