Submission #1017452

#	Time	Username	Problem	Language	Result	Execution time	Memory
1017452		cnn008	Mountains (NOI20_mountains)	C++17	100 / 100	141 ms	20236 KiB

Mountains

#include "bits/stdc++.h"
using namespace std;

#ifdef N_N_C
#include "debug.h"
#else
#define cebug(...) "Arya"
#endif

#define int long long

const int N=3e5+5;
const int mod=1e9+7;

int n,a[N],l[N],r[N],ans;
vector <int> compress;
struct BIT{
	#define gb(x) (x&(-x))
   	int n;
   	vector <int> bit;
   	void init(int _n){
   		bit.resize(_n,0);
   		n=_n;
   	}
   	void update(int pos, int val){
   		int i=pos;
      	for (; i<=n; i+=gb(i)) bit[i]+=val;
   	}
   	int get(int pos){
    	int ans=0,i=pos;
      	for (; i>=1; i-=gb(i)) ans+=bit[i];
      	return ans;
   	}
}fwl,fwr;
void sol(){
	fwl.init(N);
	fwr.init(N);
	cin>>n;
	for(int i=1; i<=n; i++) cin>>a[i],compress.push_back(a[i]);
	sort(compress.begin(),compress.end());
	compress.erase(unique(compress.begin(),compress.end()),compress.end());
	for(int i=1; i<=n; i++) a[i]=lower_bound(compress.begin(),compress.end(),a[i])-compress.begin()+1;
	for(int i=1; i<=n; i++){
		l[i]=fwl.get(a[i]-1);
		fwl.update(a[i],1);
	}
	for(int i=n; i>=1; i--){
		r[i]=fwr.get(a[i]-1);
		fwr.update(a[i],1);
		ans+=r[i]*l[i];
	}
	cout<<ans;
}
signed main(){
	ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    // freopen(".inp", "r", stdin);
    // freopen(".out", "w", stdout);
    int tt=1;
    //cin>>tt; 
    while(tt--){
    	sol();
    }
    cerr << "\nTime elapsed: " << 1000.0 * clock() / CLOCKS_PER_SEC << " ms.\n";
    return 0;
}
/**  /\_/\
*   (= ._.)
*   / >💖 \>💕
**/

Compilation message (stderr)

Mountains.cpp:67:9: warning: "/*" within comment [-Wcomment]
   67 | /**  /\_/\
      |

• Subtask 1: 2 / 2
• Subtask 2: 4 / 4
• Subtask 3: 9 / 9
• Subtask 4: 36 / 36
• Subtask 5: 28 / 28
• Subtask 6: 9 / 9
• Subtask 7: 12 / 12