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#define PROBLEM "http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=ALDS1_5_D" #include "../template.hpp" #include "../DP/InversionNumber.hpp" signed main(){ int n;cin>>n; vector<int> a(n); cin>>a; cout<<InversionNumber(a)<<endl; return 0; }
#line 1 "test/AOJ_ALDS1_5_D.test.cpp" #define PROBLEM "http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=ALDS1_5_D" #line 1 "template.hpp" #include<bits/stdc++.h> using namespace std; #define ALL(x) begin(x),end(x) #define rep(i,n) for(int i=0;i<(n);i++) #define debug(v) cout<<#v<<":";for(auto x:v){cout<<x<<' ';}cout<<endl; #define mod 1000000007 using ll=long long; const int INF=1000000000; const ll LINF=1001002003004005006ll; int dx[]={1,0,-1,0},dy[]={0,1,0,-1}; // ll gcd(ll a,ll b){return b?gcd(b,a%b):a;} template<class T>bool chmax(T &a,const T &b){if(a<b){a=b;return true;}return false;} template<class T>bool chmin(T &a,const T &b){if(b<a){a=b;return true;}return false;} struct IOSetup{ IOSetup(){ cin.tie(0); ios::sync_with_stdio(0); cout<<fixed<<setprecision(12); } } iosetup; template<typename T> ostream &operator<<(ostream &os,const vector<T>&v){ for(int i=0;i<(int)v.size();i++) os<<v[i]<<(i+1==(int)v.size()?"":" "); return os; } template<typename T> istream &operator>>(istream &is,vector<T>&v){ for(T &x:v)is>>x; return is; } #line 4 "test/AOJ_ALDS1_5_D.test.cpp" #line 1 "DP/InversionNumber.hpp" template<typename T> long long InversionNumber(vector<T> v){ vector<T> ord=v; sort(begin(ord),end(ord)); ord.erase(unique(begin(ord),end(ord)),end(ord)); vector<long long> bit(ord.size()+1,0); long long ret=0; for(int i=0;i<(int)v.size();i++){ int p=lower_bound(begin(ord),end(ord),v[i])-begin(ord)+1; for(int j=p;j;j-=(j&-j)) ret-=bit[j]; for(int j=p;j<=(int)ord.size();j+=(j&-j)) bit[j]+=1; ret+=i; } return ret; } #line 6 "test/AOJ_ALDS1_5_D.test.cpp" signed main(){ int n;cin>>n; vector<int> a(n); cin>>a; cout<<InversionNumber(a)<<endl; return 0; }