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  1. #include<bits/stdc++.h>
  2. using namespace std;
  3. typedef long long ll;
  4. const ll inf=1e15,N=2e5+5;
  5. #define pb push_back
  6. #define ff first
  7. #define ss second
  8. #define pii pair<ll,ll>
  9.  
  10. ll bit[N];
  11.  
  12. void update(ll x,ll val)
  13. {
  14. 	for(;x<N;x+=x&-x)
  15. 		bit[x]+=val;
  16. }
  17.  
  18. ll get(ll x)
  19. {
  20. 	ll ans=0;
  21. 	for(;x>0;x-=x&-x)
  22. 		ans+=bit[x];
  23. 	return ans;
  24. }
  25.  
  26. int main() {
  27. 	ll n,i,j;
  28. 	string s;
  29. 	cin >> n >> s;
  30. 	vector<ll>pos[26];
  31. 	for(i=0;i<n;i++)
  32. 		pos[s[i]-'a'].pb(i);
  33. 	ll a[n],ps[26]={0};
  34. 	reverse(s.begin(),s.end());
  35. 	for(i=0;i<s.size();i++)
  36. 	{
  37. 		ll in=s[i]-'a';
  38. 		ll ind=pos[in][ps[in]];
  39. 		a[ind]=i+1;
  40. 		ps[in]++;
  41. 	}
  42. 	/*for(i=0;i<n;i++)
  43. 		cout << a[i] <<" ";*/
  44. 	ll ans=0;
  45. 	for(i=n-1;i>=0;i--)
  46. 	{
  47. 		ans+=get(a[i]);
  48. 		update(a[i],1);
  49. 	}
  50. 	cout << ans;
  51.  
  52. return 0;
  53. }
Success #stdin #stdout 0s 4940KB
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6
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Standard output is empty
https://ideone.com/HgdFxA
language:
C++14 (gcc 8.3)
created:
3 years ago
visibility:
public

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