Timus: 1523. K-inversions

Problem Link : http://acm.timus.ru/problem.aspx?space=1&num=1523

Solution Idea:



#include <bits/stdc++.h>
//#include <ext/pb_ds/assoc_container.hpp>
//#include <ext/pb_ds/tree_policy.hpp>

#define pii              pair <int,int>
#define pll              pair <long long,long long>
#define sc               scanf
#define pf               printf
#define Pi               2*acos(0.0)
#define ms(a,b)          memset(a, b, sizeof(a))
#define pb(a)            push_back(a)
#define MP               make_pair
#define db               double
#define ll               long long
#define EPS              10E-10
#define ff               first
#define ss               second
#define sqr(x)           (x)*(x)
#define D(x)             cerr<<#x " = "<<(x)<<endl
#define VI               vector <int>
#define DBG              pf("Hi\n")
#define MOD              1000000000
#define CIN              ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define SZ(a)            (int)a.size()
#define sf(a)            scanf("%d",&a)
#define sfl(a)           scanf("%lld",&a)
#define sff(a,b)         scanf("%d %d",&a,&b)
#define sffl(a,b)        scanf("%lld %lld",&a,&b)
#define sfff(a,b,c)      scanf("%d %d %d",&a,&b,&c)
#define sfffl(a,b,c)     scanf("%lld %lld %lld",&a,&b,&c)
#define stlloop(v)       for(__typeof(v.begin()) it=v.begin();it!=v.end();it++)
#define loop(i,n)        for(int i=0;i<n;i++)
#define loop1(i,n)       for(int i=1;i<=n;i++)
#define REP(i,a,b)       for(int i=a;i<b;i++)
#define RREP(i,a,b)      for(int i=a;i>=b;i--)
#define TEST_CASE(t)     for(int z=1;z<=t;z++)
#define PRINT_CASE       printf("Case %d: ",z)
#define LINE_PRINT_CASE  printf("Case %d:\n",z)
#define CASE_PRINT       cout<<"Case "<<z<<": "
#define all(a)           a.begin(),a.end()
#define intlim           2147483648
#define infinity         (1<<28)
#define ull              unsigned long long
#define gcd(a, b)        __gcd(a, b)
#define lcm(a, b)        ((a)*((b)/gcd(a,b)))

using namespace std;

//using namespace __gnu_pbds;
//typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;


/*----------------------Graph Moves----------------*/
//const int fx[]={+1,-1,+0,+0};
//const int fy[]={+0,+0,+1,-1};
//const int fx[]={+0,+0,+1,-1,-1,+1,-1,+1};   // Kings Move
//const int fy[]={-1,+1,+0,+0,+1,+1,-1,-1};  // Kings Move
//const int fx[]={-2, -2, -1, -1,  1,  1,  2,  2};  // Knights Move
//const int fy[]={-1,  1, -2,  2, -2,  2, -1,  1}; // Knights Move
/*------------------------------------------------*/

/*-----------------------Bitmask------------------*/
//int Set(int N,int pos){return N=N | (1<<pos);}
//int reset(int N,int pos){return N= N & ~(1<<pos);}
//bool check(int N,int pos){return (bool)(N & (1<<pos));}
/*------------------------------------------------*/

#define mx 20006

ll tree[12][mx];
ll ara[mx],ara2[12][mx];

void update(int id, int idx, ll val)
{
    for(; idx<mx && idx; idx+=idx&-idx)
        tree[id][idx]+=val;
}

ll query(int id, int idx)
{
    ll ret=0;
    for(; idx; idx-=idx&-idx)
        ret+=tree[id][idx];
    return ret;
}

//vector<ll>v;

int main()
{

//    freopen("in.txt","r",stdin);
//	  freopen("out.txt","w",stdout);

    int n,k;
    sff(n,k);
//    v.pb(0);
    loop1(i,n)
    {
        sfl(ara[i]);
        ara2[1][i]=1;
//        v.pb(ara[i]);
    }
//    sort(all(v));

    ll ans=0;
    for(int j=1; j<k; j++)
    {
        for(int i=n; i>0; i--)
        {
//        int id=lower_bound(all(v),ara[i])-v.begin();
            int id=ara[i];
            ara2[j+1][i]=query(j,id)%MOD;
            update(j,id+1,ara2[j][i]);
//        update(0,id-1,-1);
        }
    }

//    for(int i=n; i>0; i--)
//    {
////        int id=lower_bound(all(v),ara[i])-v.begin();
//        int id=ara[i];
//        ans+=query(1,id);
//        update(1,id+1,ara2[i]);
////        update(1,id-1,-ara2[i]);
//    }

    for(int i=1; i<=n; i++)
        ans+=ara2[k][i];

    printf("%lld\n",ans%MOD);

    return 0;
}


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