全TLE版：

#include<bits/stdc++.h>
#define ll long long
#define ld long double
#define rep(x,a,b) for(int x=(a);x<=(b);++x)
#define rop(x,a,b) for(int x=(a);x<(b);++x)
#define per(x,a,b) for(int x=(a);x>=(b);--x)
#define pb push_back
using namespace std;

const int N = 2e5 + 10;

int read(){
	int x=0,f=1;char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
	while(ch>='0'&&ch<='9'){x=(x<<3)+(x<<1)+ch-'0';ch=getchar();}
	return x*f;
}
ll llread(){
	ll x=0,f=1;char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
	while(ch>='0'&&ch<='9'){x=(x<<3)+(x<<1)+ch-'0';ch=getchar();}
	return x*f;
}

int n, nt = 1, mapp[N], m;
int endd[N];
char ogn[N];
struct node{
	int y, id;
};
vector<node> p[N];
struct Edge{//fail -> now
	int to, nxt;
}e[N<<1];
int head[N], ecnt = 0, tot;
void addedge( int u , int v ){
	e[++ecnt] = (Edge){v,head[u]};
	head[u] = ecnt;
}
queue<int> q;
struct tree_node{
	int son[26], fail, flag, fa;
};
struct Trie{
	tree_node t[N];
	int insert( int now , char s ){
//		cout << s << "\n";
		int v = s - 'a';
		if( !t[now].son[v] ){
//		cout << now << " " << v << "\n";
			t[now].son[v] = ++nt;
			t[t[now].son[v]].fa = now;
		}	
		return t[now].son[v];
	}
	int back( int now ){return t[now].fa;}
	void ed( int now ){t[now].flag = ++tot;endd[tot] = now;}
	void get_fail(){
		for( int i = 0 ; i < 26 ; ++i )t[0].son[i] = 1;
		q.push(1);t[1].fail = 0;
		while( !q.empty() ){
			int now = q.front();q.pop();
			int fafail = t[now].fail;
			for( int i = 0 ; i < 26 ; ++i ){
				int v = t[now].son[i];
				if(!v){t[now].son[i] = t[fafail].son[i];continue;}
				t[v].fail = t[fafail].son[i];
				q.push(v);
			}
		}
	}
}AC;
struct BIT{
	int c[N];
	int lowbit( int x ){
		return x & -x;
	}
	void update( int x , int w ){
		while( x <= nt ){
			x += lowbit(x);
			c[x] += w;
		}
	}
	int query( int x ){int res = 0;while(x > 0){res += c[x];x -= lowbit(x);};}
}bit;
int dn, dfn[N], vis[N], sz[N];
int ans[N];
void dfsfail( int x ){
	dfn[x] = ++dn;vis[x] = 1;sz[x] = 1;
	for( int i = head[x] ; i ; i = e[i].nxt ){
		int v = e[i].to;
		if( !vis[v] ){
			dfsfail(v);
			sz[x] += sz[v];	
		}
	}
	return ;
}
void dfstrie( int x ){
	bit.update(dfn[x],1);
	if( AC.t[x].flag != 0 ){
		int it = AC.t[x].flag;
		for( int i = 0 ; i < p[it].size() ; ++i ){
			int f = p[it][i].y , id = p[it][i].id;
			ans[id] = bit.query(dfn[f] + sz[f] - 1) - bit.query(dfn[f] - 1);
		}
	}
	for( int i = 0 ; i < 26 ; ++i )
		if( AC.t[x].son[i] > 0 )dfstrie(AC.t[x].son[i]);
	bit.update(dfn[x],-1);
	return ; 
}
int main(){
	cin >> (ogn+1);
	n = strlen(ogn+1);
	for( int i = 1, now = 1 ; i <= n ; ++i ){
		if( ogn[i] == 'B' ){now = AC.back(now);}
		else if( ogn[i] == 'P' ){AC.ed(now);}
		else now = AC.insert(now,ogn[i]);
//		cout << i << " " << now << "\n";
	}
	m = read();
	for( int i = 1, x, y ; i <= m ; ++i ){
		x = read();y = read();
		p[y].pb((node){x,i});
	}
	for( int i = 2 ; i <= nt ; ++i )addedge(AC.t[i].fail,i);
	dfsfail(1);
	dfstrie(1);
	for( int i = 1 ; i <= m ; ++i )cout << ans[i] << "\n";
	return 0;
}

全WA版：

#include<bits/stdc++.h>
#define ll long long
#define ld long double
#define rep(x,a,b) for(int x=(a);x<=(b);++x)
#define rop(x,a,b) for(int x=(a);x<(b);++x)
#define per(x,a,b) for(int x=(a);x>=(b);--x)
#define pb push_back
using namespace std;

const int N = 2e5 + 10;

int read(){
	int x=0,f=1;char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
	while(ch>='0'&&ch<='9'){x=(x<<3)+(x<<1)+ch-'0';ch=getchar();}
	return x*f;
}
ll llread(){
	ll x=0,f=1;char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
	while(ch>='0'&&ch<='9'){x=(x<<3)+(x<<1)+ch-'0';ch=getchar();}
	return x*f;
}

int n, nt = 1, mapp[N], m;
int endd[N];
char ogn[N];
struct node{
	int y, id;
};
vector<node> p[N];
struct Edge{//fail -> now
	int to, nxt;
}e[N<<1];
int head[N], ecnt = 0, tot;
void addedge( int u , int v ){
	e[++ecnt] = (Edge){v,head[u]};
	head[u] = ecnt;
}
queue<int> q;
struct tree_node{
	int son[26], fail, flag, fa;
};
struct Trie{
	tree_node t[N];
	int insert( int now , char s ){
//		cout << s << "\n";
		int v = s - 'a';
		if( !t[now].son[v] ){
//		cout << now << " " << v << "\n";
			t[now].son[v] = ++nt;
			t[t[now].son[v]].fa = now;
		}	
		return t[now].son[v];
	}
	int back( int now ){return t[now].fa;}
	void ed( int now ){t[now].flag = ++tot;endd[tot] = now;}
	void get_fail(){
		for( int i = 0 ; i < 26 ; ++i )t[0].son[i] = 1;
		q.push(1);t[1].fail = 0;
		while( !q.empty() ){
			int now = q.front();q.pop();
			int fafail = t[now].fail;
			for( int i = 0 ; i < 26 ; ++i ){
				int v = t[now].son[i];
				if(!v){t[now].son[i] = t[fafail].son[i];continue;}
				t[v].fail = t[fafail].son[i];
				q.push(v);
			}
		}
	}
}AC;
struct BIT{
	int c[N];
	int lowbit( int x ){
		return x & -x;
	}
	void update( int x , int w ){
		while( x <= nt ){
			x += lowbit(x);
			c[x] += w;
			if( x == 0 )return ;
		}
	}
	int query( int x ){int res = 0;while(x > 0){res += c[x];x -= lowbit(x);};}
}bit;
int dn, dfn[N], vis[N], sz[N];
int ans[N];
void dfsfail( int x ){
	dfn[x] = ++dn;vis[x] = 1;sz[x] = 1;
	for( int i = head[x] ; i ; i = e[i].nxt ){
		int v = e[i].to;
		if( !vis[v] ){
			dfsfail(v);
			sz[x] += sz[v];	
		}
	}
	return ;
}
void dfstrie( int x ){
	bit.update(dfn[x],1);
	if( AC.t[x].flag != 0 ){
		int it = AC.t[x].flag;
		for( int i = 0 ; i < p[it].size() ; ++i ){
			int f = p[it][i].y , id = p[it][i].id;
			ans[id] = bit.query(dfn[f] + sz[f] - 1) - bit.query(dfn[f] - 1);
		}
	}
	for( int i = 0 ; i < 26 ; ++i )
		if( AC.t[x].son[i] > 0 )dfstrie(AC.t[x].son[i]);
	bit.update(dfn[x],-1);
	return ; 
}
int main(){
	cin >> (ogn+1);
	n = strlen(ogn+1);
	for( int i = 1, now = 1 ; i <= n ; ++i ){
		if( ogn[i] == 'B' ){now = AC.back(now);}
		else if( ogn[i] == 'P' ){AC.ed(now);}
		else now = AC.insert(now,ogn[i]);
//		cout << i << " " << now << "\n";
	}
	m = read();
	for( int i = 1, x, y ; i <= m ; ++i ){
		x = read();y = read();
		p[y].pb((node){x,i});
	}
	for( int i = 2 ; i <= nt ; ++i )addedge(AC.t[i].fail,i);
	dfsfail(1);
	dfstrie(1);
	for( int i = 1 ; i <= m ; ++i )cout << ans[i] << "\n";
	return 0;
}

不懂就问：这两种树状数组的写法为啥一个死循环，一个就能跑呢？