BZOJ 1878 [SDOI2009]HH的项链 （主席树 或 莫队算法）

题目链接  HH的项链

这道题可以直接上主席树的模板

#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 long long LL;

const int N = 5e4 + 10;

const int M = 3e6 + 10;

int n, tot, q, a[N];

int T[M], lson[M], rson[M], val[M];

int nxt[N], b[N];

int m;

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;

	}

}

int main(){

	scanf("%d", &n);

	rep(i, 1, n) scanf("%d", a + i);

	init();

	scanf("%d", &m);

	while (m--){

		int x, y;

		scanf("%d%d", &x, &y);

		printf("%d\n", ask(x, y));

	}

	return 0;

}

当然用莫队算法也是可以做的

#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 long long LL;

const int N = 2e5 + 10;

int belong[N];

int a[N], b[N], c[N], ans[N];

int n, m, l, r, cnt, BS;

int now = 0;

struct node{

	int l, r, id;

	friend bool operator < (const node &a, const node &b){

		return belong[a.l] == belong[b.l] ? belong[a.r] < belong[b.r] : belong[a.l] < belong[b.l];

	}

} q[N];

int main(){

	scanf("%d", &n);

	BS = (int)sqrt(n + 0.5);

	rep(i, 1, n) scanf("%d", a + i), b[i] = a[i];

	sort(b + 1, b + n + 1);

	cnt = unique(b + 1, b + n + 1) - b - 1;

	rep(i, 1, n) a[i] = lower_bound(b + 1, b + cnt + 1, a[i]) - b;

	scanf("%d", &m);

	rep(i, 1, m){

		scanf("%d%d", &q[i].l, &q[i].r);

		q[i].id = i;

	}

	rep(i, 1, n) belong[i] = (i - 1) / BS + 1;

	sort(q + 1, q + m + 1);

	l = 0, r = 0;

	rep(i, 1, m){

		while (l > q[i].l){ --l; if (c[a[l]] == 0) ++now; ++c[a[l]]; }

		while (r < q[i].r){ ++r; if (c[a[r]] == 0) ++now; ++c[a[r]]; }

		while (l < q[i].l){ --c[a[l]]; if (!c[a[l]]) --now; ++l; }

		while (r > q[i].r){ --c[a[r]]; if (!c[a[r]]) --now; --r; }

		ans[q[i].id] = now;

	}

	rep(i, 1, m) printf("%d\n", ans[i]);

	return 0;

}