线段树维护字符串哈希

zhujio / 2024-02-09 / 原文

[ABC331F] Palindrome Query

#include <bits/stdc++.h>
using namespace std;
#define endl "\n"
#define int long long
typedef long long ll;

const int base = 131;
const int p1 = 1222827239;
const int N = 1e6 + 100;

int n, q, pn[N];
string s;

struct node {
    int lsum, rsum, len;
    node() {lsum = rsum = 0;}
} Seg[N * 4];

node operator + (const node &l, const node &r) {
    node ans;
    ans.lsum = (l.lsum + pn[l.len] * r.lsum % p1) % p1;
    ans.rsum = (r.rsum + pn[r.len] * l.rsum % p1) % p1;
    ans.len = l.len + r.len;
    return ans;
}

void pushup(int id) {
    Seg[id] = Seg[id * 2] + Seg[id * 2 + 1];
}

void build(int id, int l, int r) {
    Seg[id].len = r - l + 1;
    if (l == r) {
        Seg[id].lsum = Seg[id].rsum = s[l];
        return;
    }
    int mid = l + r >> 1;
    build(id * 2, l, mid); build(id * 2 + 1, mid + 1, r);
    pushup(id);
}    

void modify(int id, int l, int r, int pos, char c) {
    if (l == r) {
        Seg[id].lsum = Seg[id].rsum = c;
        return;
    }
    int mid = l + r >> 1;
    if (pos <= mid) modify(id * 2, l, mid, pos, c);
    else modify(id * 2 + 1, mid + 1, r, pos, c);
    pushup(id);
}

node query(int id, int l, int r, int x, int y) {
    if (x <= l && y >= r) return Seg[id];
    int mid = l + r >> 1;
    if (y <= mid) return query(id * 2, l, mid, x, y);
    if (x > mid) return query(id * 2 + 1, mid + 1, r, x, y);
    return query(id * 2, l, mid, x, y) + query(id * 2 + 1, mid + 1, r, x, y);
}

void solve() {
    cin >> n >> q >> s;
    
    s = " " + s;
    pn[0] = 1;
    for (int i = 1; i <= n; i++) pn[i] = pn[i - 1] * 1ll * base % p1;

    build(1, 1, n);

    while (q--) {
        int op; cin >> op;
        if (op == 1) {
            int pos; cin >> pos;
            char c; cin >> c;
            modify(1, 1, n, pos, c);
        } else {
            int l, r; cin >> l >> r;
            node ans = query(1, 1, n, l, r);
            if (ans.lsum == ans.rsum) cout << "Yes" << endl;
            else cout << "No" << endl;            
        }
    }
}    

signed main() {
    ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);

    // int T = 1; cin >> T;
    // while(T--) solve();
    solve();

    return 0;    
}