bzoj 3289 莫队 逆序对

莫队维护逆序对，区间左右增减要分类讨论。

记得离散化。

 /**************************************************************
     Problem: 3289
     User: idy002
     Language: C++
     Result: Accepted
     Time:5480 ms
     Memory:3164 kb
 ****************************************************************/

 #include <cstdio>
 #include <cstring>
 #include <cmath>
 #include <algorithm>
 #define maxn 50010
 #define lowbit(i) ((i)&(-(i)))
 using namespace std;

 typedef long long lng;

 int n, m;
 int disc[maxn];
 int lx[maxn], rx[maxn], mccno[maxn], stot;
 int w[maxn];
 lng cnt[maxn], cnttot, cur_ans;
 lng ans[maxn];

 struct Qu {
     int l, r, id;
     bool operator<( const Qu & b ) const {
         return mccno[l]<mccno[b.l] || (mccno[l]==mccno[b.l] && r<b.r );
     }
 };
 Qu qu[maxn];

 lng qu_pres( int r ) {
     lng rt = ;
     for( int i=r; i; i-=lowbit(i) )
         rt += cnt[i];
     return rt;
 }
 void up_val( int pos, int delta ) {
     for( int i=pos; i<=n; i+=lowbit(i) )
         cnt[i] += delta;
     cnttot += delta;
 }
 void push_back( int pos ) {
     cur_ans += cnttot - qu_pres( pos );
     up_val( pos, + );
 }
 void pop_back( int pos ) {
     cur_ans -= cnttot - qu_pres( pos );
     up_val( pos, - );
 }
 void push_front( int pos ) {
     cur_ans += qu_pres( pos- );
     up_val( pos, + );
 }
 void pop_front( int pos ) {
     cur_ans -= qu_pres( pos- );
     up_val( pos, - );
 }

 void partition() {
     int len = (int)ceil(sqrt(n))+;
     int stot = n/len;
     rx[] = ;
     for( int i=; i<=stot; i++ ) {
         lx[i] = rx[i-]+;
         rx[i] = rx[i-]+len;
     }
     if( rx[stot]!=n ) {
         stot++;
         lx[stot] = rx[stot-]+;
         rx[stot] = n;
     }
     for( int i=; i<=stot; i++ )
         for( int j=lx[i]; j<=rx[i]; j++ )
             mccno[j] = i;
 }
 void work() {
     sort( qu+, qu++m );
     int lf, rg;
     for( int q=; q<=m; q++ ) {
         if( q== || mccno[qu[q].l] != mccno[qu[q-].l] ) {
             lf = qu[q].l;
             rg = qu[q].l-;
             memset( cnt, , sizeof(cnt) );
             cur_ans = cnttot = ;
         }
         while( lf<qu[q].l ) pop_front( w[lf++] );
         while( lf>qu[q].l ) push_front( w[--lf] );
         while( rg<qu[q].r ) push_back( w[++rg] );
         while( rg>qu[q].r ) pop_back( w[rg--] );
         ans[qu[q].id] = cur_ans;
     }
 }
 int main() {
     scanf( "%d", &n );
     for( int i=; i<=n; i++ ) {
         scanf( "%d", w+i );
         disc[i] = w[i];
     }
     sort( disc+, disc++n );
     for( int i=; i<=n; i++ )
         w[i] = lower_bound( disc+, disc++n, w[i] ) - disc;
     scanf( "%d", &m );
     for( int i=; i<=m; i++ ) {
         scanf( "%d%d", &qu[i].l, &qu[i].r );
         qu[i].id = i;
     }
     partition();
     work();
     for( int i=; i<=m; i++ )
         printf( "%lld\n", ans[i] );
 }