BZOJ 1878 [SDOI2009]HH的项链

莫队算法。

#include<cstdio>
#include<cstring>
#include<cmath>
#include<queue>
#include<algorithm>
using namespace std;

const int maxn = 50000 + 10;
int cnt[1000000 + 10];
int a[maxn], pos[maxn];
int n, m, Ans, L, R;
struct X
{
    int l, r, id;
    int ans;
}s[200000 + 10];
int ans[200000 + 10];

bool cmp(const X&a, const X&b)
{
    if (pos[a.l] == pos[b.l]) return a.r<b.r;
    return a.l<b.l;
}

bool cmp1(const X&a, const X&b)
{
    return a.id<b.id;
}

int main()
{
    while (~scanf("%d", &n)) {
        int sz = sqrt(n); memset(cnt, 0, sizeof cnt);
        for (int i = 1; i <= n; i++)
        {
            scanf("%d", &a[i]);
            pos[i] = i / sz;
        }
        scanf("%d", &m);
        for (int i = 1; i <= m; i++)
        {
            scanf("%d%d", &s[i].l, &s[i].r);
            s[i].id = i;
        }
        sort(s + 1, s + m + 1, cmp);
        Ans = 0;
        for (int i = s[1].l; i <= s[1].r; i++)
        {
            cnt[a[i]]++;
            if (cnt[a[i]] == 1) Ans++;
        }
        ans[s[1].id] = Ans;
        L = s[1].l; R = s[1].r;

        for (int i = 2; i <= m; i++)
        {
            while (L < s[i].l)
            {
                cnt[a[L]]--;
                if (cnt[a[L]] == 0) Ans--;
                L++;
            }

            while (L > s[i].l)
            {
                L--;
                cnt[a[L]]++;
                if (cnt[a[L]] == 1) Ans++;
            }

            while (R > s[i].r)
            {
                cnt[a[R]]--;
                if (cnt[a[R]] == 0) Ans--;
                R--;
            }

            while (R < s[i].r)
            {
                R++;
                cnt[a[R]]++;
                if (cnt[a[R]] == 1) Ans++;
            }
            s[i].ans = Ans;
            ans[s[i].id] = Ans;
        }

        for (int i = 1; i <= m; i++)
            printf("%d\n", ans[i]);
    }
    return 0;
}