Atcoder-abc331-F - Palindrome Query——字符串哈希+线段树

 

// 简要原理
string s,t;
const ull P=131;
vector<ull> pre(n+1);       // pre[x] = pow(P,x);
h1(s+t) = h1(s)*pre[t.length()] + h1(t);
h2(s+t) = h2(t)*pre[s.length()] + h2(s);

 

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
#define endl '\n'
#define lc p<<1
#define rc p<<1|1
const ull P=131;
const int N=1e6+10;
vector<ull> pre;
string str;

struct node
{
    int l,r;
    ull h1,h2;
}tr[4*N];

void pushup(int p)
{
    int len1=tr[lc].r-tr[lc].l+1;
    int len2=tr[rc].r-tr[rc].l+1;
    tr[p].h1=tr[lc].h1*pre[len2]+tr[rc].h1;
    tr[p].h2=tr[rc].h2*pre[len1]+tr[lc].h2;
}

void build(int p, int x, int y)
{
    tr[p]={x,y,str[x],str[x]};
    if(x==y)
        return;
    int mid=x+y>>1;
    build(lc,x,mid);
    build(rc,mid+1,y);
    pushup(p);
}

void update(int p, int x, ull k)
{
    if(tr[p].l==tr[p].r)
    {
        tr[p].h1=tr[p].h2=k;
        return;
    }
    int mid=tr[p].l+tr[p].r>>1;
    if(x<=mid)  update(lc,x,k);
    else        update(rc,x,k);
    pushup(p);
}

vector<ull> query(int p, int x, int y)
{
    if(x<=tr[p].l && tr[p].r<=y)
        return {tr[p].h1,tr[p].h2,tr[p].r-tr[p].l+1};
    int mid=tr[p].l+tr[p].r>>1;
    if(x>mid)   return query(rc,x,y);
    if(y<=mid)  return query(lc,x,y);
    auto wl=query(lc,x,y);
    auto wr=query(rc,x,y);
    vector<ull> res(3);
    int len1=wl[2], len2=wr[2];
    res[0]=wl[0]*pre[len2]+wr[0];       // h1
    res[1]=wr[1]*pre[len1]+wl[1];       // h2
    res[2]=len1+len2;                   // len
    return res;
}

int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0),cout.tie(0);
    int n,m;
    cin>>n>>m>>str;
    str=' '+str;
    n++;
    pre.resize(n+1);
    pre[0]=1;
    for(int i=1;i<=n;i++)
        pre[i]=pre[i-1]*P;
    build(1,1,n);
    while(m--)
    {
        char ch;
        int opt,k,l,r;
        cin>>opt;
        if(opt==1)
        {
            cin>>k>>ch;
            update(1,k,ch);
        }
        else
        {
            cin>>l>>r;
            auto x=query(1,l,r);
            cout<<(x[0]==x[1] ? "Yes" : "No")<<endl;
        }
    }
}