Finally finished Jiayuan sister series

Suffix array + RMQ + chairman tree

This problem is to find the LCS in two segment substrings

Of course, LCS can be calculated by LCP

Set up SA first

Get a,b,c,d and get rk-c

Binary LCS set query mid

Because the LCP of two strings is min of rk1-rk2

Building ST tables

Using RMQ to find out the interval L,R that rkc can cover

It's obvious at this timeIt's legal to appear in L-R

So easy to get interval version query

Just set up the tree query node

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
using namespace std;
const int N=1e6+1000;
char S[N];
int x[N];
int y[N];
int c[N];
int SA[N];
int n,m;
void Get_SA(){
	for(int i=1;i<=n;++i)x[i]=S[i];
	for(int i=1;i<=n;++i)++c[x[i]];
	for(int i=1;i<=m;++i)c[i]+=c[i-1];
	for(int i=n;i>=1;i--)SA[c[x[i]]--]=i;
	for(int k=1;k<=n;k=k<<1){
		int num=0;
		for(int i=n-k+1;i<=n;++i)y[++num]=i;
		for(int i=1;i<=n;++i)if(SA[i]>k)y[++num]=SA[i]-k;
		for(int i=1;i<=m;++i)c[i]=0;
		for(int i=1;i<=n;++i)++c[x[i]];
		for(int i=1;i<=m;++i)c[i]+=c[i-1];
		for(int i=n;i>=1;--i)SA[c[x[y[i]]]--]=y[i],y[i]=0;
		swap(x,y);
		num=1;
		x[SA[1]]=1;
		for(int i=2;i<=n;++i)x[SA[i]]=(y[SA[i]]==y[SA[i-1]]&&y[SA[i]+k]==y[SA[i-1]+k])?num:++num;
		if(n==num)break;
		m=num;
	} 
} 
int rk[N]={};
int height[N]={};
void Get_Height(){
	for(int i=1;i<=n;++i)rk[SA[i]]=i;
	int k=0;
	for(int i=1;i<=n;++i){
		if(rk[i]==1)continue;
		if(k)k--;
		int Id=SA[rk[i]-1];
		while(Id+k<=n&&i+k<=n&&S[Id+k]==S[i+k])++k;
		height[rk[i]]=k;
	}
}
int st[N][20]={};
void Get_RMQ(){
	memset(st,0x3f,sizeof(st));
	for(int i=1;i<=n;++i){
		st[i][0]=height[i];
	}
	for(int j=1;j<=20;++j)
		for(int i=1;i<=n;++i){
			if(i+(1<<(j-1))>n)break;
			st[i][j]=min(st[i][j-1],st[i+(1<<(j-1))][j-1]);
		}
			
}
int lson[N*10]={};
int rson[N*10]={};
int root[N]={};
int sum[N*10]={};
int cnt=0;
void Update(int x,int &y,int l,int r,int pos){
	y=++cnt;
	lson[y]=lson[x];
	rson[y]=rson[x];
	sum[y]=sum[x]+1;
	if(l==r)return;
	int mid=(l+r)/2;
	if(pos<=mid)
		Update(lson[x],lson[y],l,mid,pos);
	else Update(rson[x],rson[y],mid+1,r,pos);
} 
int Query(int x,int y,int l,int r,int dl,int dr){
	if(dl<=l&&r<=dr){
		return sum[y]-sum[x];
	}
	int mid=(l+r)/2;
	int ret=0;
	if(dl<=mid)ret+=Query(lson[x],lson[y],l,mid,dl,dr);
	if(mid< dr)ret+=Query(rson[x],rson[y],mid+1,r,dl,dr);
	return ret;
}
int main(){
	int Q;
//	freopen("test.in","r",stdin);
//	freopen("test.out","w",stdout);
	scanf("%d%d",&n,&Q);
	scanf("%s",S+1);
	m=200;
	Get_SA();
	Get_Height();
	Get_RMQ();
	for(int i=1;i<=n;++i)Update(root[i-1],root[i],1,n,rk[i]);
	while(Q--){
		int a,b,c,d;
		scanf("%d%d%d%d",&a,&b,&c,&d);
		int l=1;
		int r=min((b-a+1),(d-c+1));
		int ans=0;
		while(l<=r){
			int L,R;
			L=R=rk[c];
			int mid=(l+r)/2;
			for(int i=20;i>=0;i--)if(L-(1<<i)>=0&&st[L-(1<<i)+1][i]>=mid)L=L-(1<<i); 
			for(int i=20;i>=0;i--)if(R+(1<<i)<=n&&st[R+1][i]>=mid)R=R+(1<<i);
			if(Query(root[a-1],root[b-mid+1],1,n,L,R)>0)ans=mid,l=mid+1;
			else r=mid-1;
		}
		cout<<ans<<'\n';
	}
}