不清楚，只有wa，线段树

#include <bits/stdc++.h>
#define ls k<<1
#define rs k<<1|1
using namespace std;

const int N=5e5+5;

int n,q;
string s;

struct node{
	int s,lm,rm,l,r;
}t[N*4];

node operator + (const node& l,const node& r){
	bool cnt=(s[l.r]==s[r.l]);
	return{
		max(max(l.s,r.s),(cnt)*(l.rm+r.lm)),
		max(l.lm,(cnt)*(l.s==l.r-l.l+1)*(l.s+r.lm)),
		max(r.rm,(cnt)*(r.s==r.r-r.l+1)*(r.s+l.rm)),
		l.l,
		r.r
	};
}

void pushup(int k){
	t[k]=t[ls]+t[rs];
}

void build(int k,int l,int r){
	t[k]={1,1,1,l,r};
	if(l==r)return;
	int mid=(l+r)/2;
	build(ls,l,mid);
	build(rs,mid+1,r);
	pushup(k);
	//cout<<l<<" "<<r<<" "<<t[k].s<<" "<<t[k].lm<<" "<<t[k].rm<<"\n";
}

void assign(int k,int l,int r,int a){
	if(l==r)return;
	int mid=(l+r)/2;
	if(a<=mid)assign(ls,l,mid,a);
	else assign(rs,mid+1,r,a);
	pushup(k);
}

node query(int k,int l,int r,int a,int b){
	if(a<=l&&r<=b)return t[k];
	int mid=(l+r)/2;
	node cntl={0,0,0,0,0},cntr={0,0,0,0,0},ans={0,0,0,0,0};
	if(a<=mid)cntl=query(ls,l,mid,a,b);
	else if(b>mid)cntr=query(rs,mid+1,r,a,b);
	ans=cntl+cntr;
	return ans;
}

int main(){
	cin.tie(0);
	cout.tie(0);
	ios::sync_with_stdio(false);
	cin>>n>>q>>s;
	s=" "+s;
	build(1,1,n);
	while(q--){
		int t,x;
		cin>>t>>x;
		if(t==1){
			char y;
			cin>>y;
			s[x]=y;
			assign(1,1,n,x);
		}
		else{
			int y;
			cin>>y;
			cout<<query(1,1,n,x,y).s<<"\n";
		}
	}
}