rt，在 P1972 [SDOI2009] HH的项链 中，如果对 $c$ 进行 Hash 则可以使用莫队过，反之会被卡掉 40 分 代码如下

#include <bits/stdc++.h>
#define re register
using namespace std;

constexpr int mod=2000007;
constexpr int qt = 1024;

inline int read(){
	int f = 1,x = 0;
	char ch = getchar();
	while(!isdigit(ch)){
		ch = getchar();
	}
	while(isdigit(ch)){
		x = (x << 1) + (x << 3) + (ch ^ 48);
		ch = getchar();
	}
	return x * f;
}
inline void print(int x){
	if(x > 9)print(x / 10);
	putchar(x % 10 + '0');
}

const int N = 1000001;

int n, a[N], cnt[N], ans[N];

struct node{
	int l, r, id;
}q[N];

signed main(){
	n = read();
	for(re int i = 1;i <= n;++i)	
		a[i] = read();
	re int m = read();
	for(re int i = 1;i <= m;++i){
		q[i].l = read(), q[i].r = read(), q[i].id = i;
	}
	std::sort(q + 1, q + m + 1, [](const node aa, const node bb){
        return ((aa.l / qt) == (bb.l / qt)) ? (((aa.l / qt) & 1) ? aa.r < bb.r : aa.r > bb.r) : aa.l < bb.l;
    });
	re int l = q[1].l, r = q[1].l - 1, now = 0;
	for(re int i = 1;i <= m;++i){
		while(l < q[i].l) now -= !--cnt[a[l++]];
		while(l > q[i].l) now += !cnt[a[--l]]++;
		while(r < q[i].r) now += !cnt[a[++r]]++;
		while(r > q[i].r) now -= !--cnt[a[r--]];
		ans[q[i].id] = now;
	}
	for(int i = 1;i <= m;++i)
		print(ans[i]), putchar('\n');
	return 0;
}

以上是没有 Hash 的代码 $60\ point$。 进行 Hash。

#include <bits/stdc++.h>
#define re register
using namespace std;

const int mod=2000007;
const int qt = 1024;

inline int read(){
	int f = 1,x = 0;
	char ch = getchar();
	while(!isdigit(ch)){
		ch = getchar();
	}
	while(isdigit(ch)){
		x = (x << 1) + (x << 3) + (ch ^ 48);
		ch = getchar();
	}
	return x * f;
}
inline void print(int x){
	if(x > 9)print(x / 10);
	putchar(x % 10 + '0');
}

struct HASH{
    int id[mod], val[mod], cnt;
    int find(int x){
        int z = x % mod;
        while(id[z]){if(id[z] == x){return val[z];}++z;}
        return id[z] = x, val[z] = ++cnt;
    }
}Hash;

const int N = 1000001;

int n, a[N], ans[N];

struct node{
	int l, r, id;
}q[N];

vector<int> cnt(N);

signed main(){
	n = read();
	for(re int i = 1;i <= n;++i)	
		a[i] = read(), a[i] = Hash.find(a[i]);
	re int m = read();
	for(re int i = 1;i <= m;++i){
		q[i].l = read(), q[i].r = read(), q[i].id = i;
	}
	std::sort(q + 1, q + m + 1, [](const node aa, const node bb){
        return ((aa.l / qt) == (bb.l / qt)) ? (((aa.l / qt) & 1) ? aa.r < bb.r : aa.r > bb.r) : aa.l < bb.l;
    });
	re int l = q[1].l, r = q[1].l - 1, now = 0;
	for(re int i = 1;i <= m;++i){
		while(l < q[i].l) now -= !--cnt[a[l++]];
		while(l > q[i].l) now += !cnt[a[--l]]++;
		while(r < q[i].r) now += !cnt[a[++r]]++;
		while(r > q[i].r) now -= !--cnt[a[r--]];
		ans[q[i].id] = now;
	}
	for(int i = 1;i <= m;++i)
		print(ans[i]), putchar('\n');
	return 0;
}

可以拿到 100 分