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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. int main() {
  5. 	// your code goes here
  6. 	int n;
  7. 	cin>>n;
  8. 	vector<int>a(n);
  9. 	int sum=0;
  10. 	for(int i=0;i<n;i++) {cin>>a[i];sum+=a[i];}
  11. 	// if(sum&1) return false;
  12. 	// int cnt=0;
  13. 	// int x=a[0];
  14. 	// sum-=x;
  15. 	// else{
  16. 	// 	for(int i=1;i<n-1;i++){
  17. 	// 		if(x==sum) cnt++;
  18. 	// 		sum-=a[i];
  19. 	// 		x+=a[i];
  20. 	// 	}
  21. 	// }
  22. 	unordered_map<int,int>freq;
  23. 	int pref=0;
  24. 	for(int i=0;i<n-1;i++){
  25. 		pref+=a[i];
  26. 		freq[pref]++;
  27. 	}
  28. 	int cnt=0;
  29. 	if(sum%3!=0) return false;
  30.  
  31. 	else{
  32. 		int y=sum/3;
  33. 	    int suff=a[n-1];
  34.  
  35. 		for(int i=n-2;i>=2;i--){
  36. 			if(suff==y && pref==2*y){
  37. 				cnt+=freq[y];
  38. 			}
  39. 			suff+=a[i];
  40. 			freq[pref]--;
  41. 			pref-=a[i];
  42. 		}
  43. 	}
  44. 	cout<<cnt<<endl;
  45.  
  46.  
  47. 	return 0;
  48. }
Success #stdin #stdout 0s 5316KB
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https://ideone.com/U1500R
language:
C++14 (gcc 8.3)
created:
55 minutes ago
visibility:
public

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