BZOJ-2038 小Z的袜子(hose)

小Z的袜子(hose)

莫队 板子题

在 add 和 del 上边得先删除原本的，再添加新的

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cmath>
using namespace std;
#define endl '\n'
typedef long long ll;
const int maxn = 5e4 + 10;
int num[maxn], pos[maxn];
ll up[maxn], down[maxn], ans = 0, cnt[maxn];

struct node
{
    int l, r, id;
    node(){}
    node(int _l, int _r, int _id){id = _id; l = _l; r = _r;}
}seg[maxn];

bool cmp(const node& a, const node& b)
{
    return pos[a.l] ^ pos[b.l] ? pos[a.l] < pos[b.l] : (pos[a.l] & 1 ? a.r > b.r : a.r < b.r);
}

ll gcd(ll a, ll b)
{
    return b == 0 ? a : gcd(b, a % b);
}

inline void add(int x)
{
    int now = num[x];
    if(cnt[now]) ans -= cnt[now] * (cnt[now] - 1) / 2;
    cnt[now]++;
    ans += cnt[now] * (cnt[now] - 1) / 2;
}

inline void del(int x)
{
    int now = num[x];
    ans -= cnt[now] * (cnt[now] - 1) / 2;
    cnt[now]--;
    if(cnt[now]) ans += cnt[now] * (cnt[now] - 1) / 2;
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int n, m;
    cin >> n >> m;
    for(int i=1; i<=n; i++) cin >> num[i];
    for(int i=0; i<m; i++)
    {
        int x, y;
        cin >> x >> y;
        seg[i] = node(x, y, i);
    }
    int t = sqrt(n);
    for(int i=0; i<=n; i++) pos[i] = i / t;
    sort(seg, seg + m, cmp);
    int l = 1, r = 0;
    for(int i=0; i<m; i++)
    {
        while(seg[i].l < l) add(--l);
        while(seg[i].r > r) add(++r);
        while(seg[i].l > l) del(l++);
        while(seg[i].r < r) del(r--);
        up[seg[i].id] = ans;
        ll x = r - l + 1;
        down[seg[i].id] = x * (x - 1) / 2;
    }

    for(int i=0; i<m; i++)
    {
        if(up[i] == 0) {cout << 0 << "/" << 1 << endl; continue;}
        ll x = gcd(down[i], up[i]);
        up[i] /= x;
        down[i] /= x;
        cout << up[i] << "/" << down[i] << endl;
    }
    return 0;
}