SPOJ3276 D-query

题意：n个数 a₁...a_n，q组询问，每组询问给定 l，r，输出 [ l, r ] 有多少不同的数 ( n ≤30000, q ≤200000, a_i ≤ 10⁶ )

离线 + 树状数组维护

 #include<bits/stdc++.h>

 using namespace std;

 const int MAXN = ;
 int n, a[MAXN], start[MAXN], nex[MAXN], q, t[MAXN], an[MAXN], k[MAXN];
 pair<int, int> Q[MAXN];

 template <typename tn> void read (tn & a) {
     tn x = , f = ;
     char c = getchar();
     while (c < '' || c > ''){ if (c == '-') f = -; c = getchar(); }
     while (c >= '' && c <= ''){ x = x *  + c - ''; c = getchar(); }
     a = f ==  ? x : -x;
 }

 void add (int k, int d) {
     while (k <= n) {
         t[k] += d;
         k += k & -k;
     }
 }

 int sum (int k) {
     int s = ;
     while (k > ) {
         s += t[k];
         k -= k & -k;
     }
     return s;
 }

 bool cmp (const int &i, const int & j) {
     return Q[i] < Q[j];
 }

 int main() {
     read(n);
     for (int i = ; i <= n; ++i) {
         read(a[i]);
     }
     for (int i = n; i >= ; --i) {
         if (start[a[i]] != ) add(start[a[i]], -);
         add(i, );
         nex[i] = start[a[i]];
         start[a[i]] = i;
     }
     read(q);
     for (int i = ; i <= q; ++i) {
         read(Q[i].first);
         read(Q[i].second);
     }
     for (int i = ; i <= q; ++i) k[i] = i;
     sort(k + , k +  + q, cmp);
     int lx = ;
     for (int i = ; i <= q; ++i) {
         while (Q[k[i]].first > lx) {
             if (sum(lx) - sum(lx - ) > ) {
                 if (nex[lx] != ) add(nex[lx], );
                 add(lx, -);
             }
             ++lx;
         }
         an[k[i]] = sum(Q[k[i]].second) - sum(Q[k[i]].first - );
     }
     for (int i = ; i <= q; ++i) printf("%d ", an[i]); printf("\n");
     return ;
 }