Problem Link : http://www.spoj.com/problems/TRIPINV/
Solution Idea:
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Same as Codeforces: 61 E. Enemy is weak
#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 1000000007 #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 100006 ll tree[2][mx]; ll ara[mx],ara2[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; sf(n); // v.pb(0); loop1(i,n) { sfl(ara[i]); // v.pb(ara[i]); } // sort(all(v)); ll ans=0; for(int i=n; i>0; i--) { // int id=lower_bound(all(v),ara[i])-v.begin(); int id=ara[i]; ara2[i]=query(0,id); update(0,id+1,1); // 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]); } printf("%lld\n",ans); return 0; }