P2709 小B的询问 （莫队算法）

题意：
题解：莫队算法
第一道莫队，莫队算法主要是能处理离线区间查询问题。

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include<cstdio>
#include<string>
#include<cstring>
#include<algorithm>
#include<queue>
#include<stack>
#include<cmath>
#include<vector>
#include<fstream>
#include<set>
#include<map>
#include<sstream>
#include<iomanip>
#define ll long long
using namespace std;
const int maxn = 5e4 + 5;
int block, res, belong[maxn], cnt[maxn], ans[maxn];
struct node {
    
    
    int l, r, id;
    bool operator < (const node& b) const {
    
    
        if (belong[l] == belong[b.l]) return r < b.r;
        else return belong[l] < belong[b.l];
    }
}q[maxn];
void add(int x) {
    
    
    res -= cnt[x] * cnt[x];
    ++cnt[x];
    res += cnt[x] * cnt[x];
}
void del(int x) {
    
    
    res -= cnt[x] * cnt[x];
    --cnt[x];
    res += cnt[x] * cnt[x];
}
int n, m, k, a[maxn], l, r;
int main() {
    
    
	scanf("%d%d%d", &n, &m, &k);
    block = sqrt(n);
    for (int i = 1; i <= n; i++) {
    
    
        scanf("%d", &a[i]);
        belong[i] = (i - 1) / block + 1;
    }
    for (int i = 1; i <= m; i++) scanf("%d%d", &q[i].l, &q[i].r), q[i].id = i;
    sort(q + 1, q + m + 1);
    res = 0, l = 1, r = 0;
    for (int i = 1; i <= m; i++) {
    
    
        while (l < q[i].l) del(a[l++]);
        while (l > q[i].l) add(a[--l]);
        while (r > q[i].r) del(a[r--]);
        while (r < q[i].r) add(a[++r]);
        ans[q[i].id] = res;
    }
    for (int i = 1; i <= m; i++) printf("%d\n", ans[i]);
	return 0;
}