HDU 5790 Prefix（Hash + 主席树）

题目链接  Prefix

题意  给定一个字符串序列，求第$l$个字符串到第$r$个字符串之间有多少个不同的前缀

强制在线

考虑$Hash$

首先把所有前缀都$hash$出来，按顺序组成一个长度不超过$10^{5}$的序列。

然后放入主席树，问题转化为查询区间内不同数字的个数。

查询的时候找到的起始字符串的开头和终止字符串的结尾就可以了。

#include <bits/stdc++.h>

using namespace std;

#define rep(i, a, b)    for (int i(a); i <= (b); ++i)
#define dec(i, a, b)    for (int i(a); i >= (b); --i)

typedef unsigned long long ULL;

const int N = 1e5 + 10;
const int M = 4e6 + 10;

ULL a[N], b[N], val[M], g[200];
int c[N], d[N], T[M], lson[M], rson[M], nxt[N], idx, len, n, tot, nn, Z;
char st[N];

int build(int l, int r){
	int rt = tot++;
	val[rt] = 0;
	int m = (l + r) >> 1;
	if(l != r){
		lson[rt] = build(l, m);
		rson[rt] = build(m + 1, r);
	}
	return rt;
}

int update(int rt, int pos, int v){
	int newrt = tot++, tmp = newrt;
	int l = 1, r = n;
	val[newrt] = val[rt] + v;
	while(l < r)
	{
		int m = (l + r) >> 1;
		if(pos <= m)
		{
			lson[newrt] = tot++;
			rson[newrt] = rson[rt];
			newrt = lson[newrt];
			rt = lson[rt];
			r = m;
		}
		else
		{
			rson[newrt] = tot++;
			lson[newrt] = lson[rt];
			newrt = rson[newrt];
			rt = rson[rt];
			l = m + 1;
		}
		val[newrt] = val[rt] + v;
	}
	return tmp;
}

int query(int rt, int pos){
	int ret = 0;
	int l = 1, r = n;
	while(pos > l){
		int m = (l + r) >> 1;
		if (pos <= m){
			ret += val[rson[rt]];
			rt = lson[rt];
			r = m;
		}
		else{
			l = m + 1;
			rt = rson[rt];
		}
	}
	return ret + val[rt];
}

int ask(int l, int r){ return query(T[r], l); }

void init(){
	tot = 0;
	memset(nxt, -1, sizeof(nxt));
	rep(i, 1, n) b[i - 1] = a[i];
	sort(b, b + n);
	int cnt = unique(b, b + n) - b;
	T[0] = build(1, n);
	rep(i, 1, n){
		int id = lower_bound(b, b + cnt, a[i]) - b;
		if(nxt[id] == -1)
			T[i] = update(T[i - 1], i, 1);
		else{
			int t = update(T[i - 1], nxt[id], -1);
			T[i] = update(t, i, 1);
		}
		nxt[id] = i;
	}

}

inline ULL get(char ch){ return g[(int)ch - 97]; }

int main(){

	srand(time(NULL));
	rep(i, 0, 100){
		int yy = rand() % 3 + 1;
		g[i] = 1;
		rep(j, 1, yy) g[i] *= rand();
	}

	while (~scanf("%d", &nn)){
		Z = 0;
		n = 0;
		rep(i, 1, nn){
			scanf("%s", st);
			len = strlen(st);
			ULL haha = 0LL;
			rep(j, 0, len - 1){
				++n;
				haha = haha * 233LL + 6843 * get(st[j]);
				a[n] = haha;
			}

			c[i] = d[i - 1] + 1;
			d[i] = n;

		}

		init();
		int q;
		scanf("%d", &q);
		Z = 0;
		while (q--){
			int x, y;
			scanf("%d%d", &x, &y);
			int ll = (Z + x) % nn + 1;
			int rr = (Z + y) % nn + 1;
			if (ll > rr) swap(ll, rr);
			printf("%d\n", Z = ask(c[ll], d[rr]));
		}

	}

	return 0;

}