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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3. using ll =long long;
  4. int main() {
  5. 	// your code goes here
  6. 	ll n;
  7. 	cin>>n;
  8. 	vector<ll>a(n);
  9. 	for(ll i=0;i<n;i++) cin>>a[i];
  10. 	unordered_map<int,int> prefFreq;
  11. 	unordered_map<int,int> suffFreq;
  12. 	int sum=0;
  13. 	for(int i=0;i<n;i++)  sum+=a[i];
  14. 	int cnt=0;
  15. 	if(sum%4!=0){
  16. 		cout<<0<<endl;
  17. 		return 0;
  18. 	}
  19. 	else{
  20. 		ll pref=a[0];
  21. 		prefFreq[a[0]]=1;
  22.  
  23. 		ll suff=0;
  24. 		for(ll i=n-1;i>=3;i--){
  25. 			suff+=a[i];
  26. 			suffFreq[suff]++;
  27. 		}
  28. 		suff+=a[2];
  29. 		pref+=a[1];
  30. 		ll y=sum/4;
  31. 		for(int i=1;i<=n-3;i++){
  32. 			if(pref==2*y && suff==2*y){
  33. 				//1st and 4 quater
  34. 				cnt+=(prefFreq[y]*suffFreq[y]);
  35. 				// cout<<cnt<<" "<<i<<endl;
  36. 			}
  37. 			prefFreq[pref]++;
  38. 			pref+=a[i+1];
  39. 			suff-=a[i+1];
  40. 			suffFreq[suff]--;
  41.  
  42. 		}
  43. 	}
  44. 	cout<<endl;
  45. 	cout<<cnt<<endl;
  46. 	return 0;
  47. }
Success #stdin #stdout 0s 5320KB
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stdin
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7
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stdout
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https://ideone.com/Q4lKC4
language:
C++14 (gcc 8.3)
created:
1 day ago
visibility:
public

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