題目鏈接 HH的項鏈

這道題可以直接上主席樹的模板

#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;

}  

當然用莫隊算法也是可以做的

#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;
}

BZOJ 1878 [SDOI2009]HH的項鏈 （主席樹 或 莫隊算法）