#include <bits/stdc++.h> using namespace std; #define endl '\n' #define st first #define nd second #define pb push_back #define sz(x) (int)(x).size() #define all(x) (x).begin(), (x).end() #define ll long long ll mod=1000000007; int inf=1000000007; ll infl=1000000000000000007; const int N=200007; vector<int>V[200]; int side[N]; int p[N]; int BIT[N]; int que(int x) { int s=0; for (;x;x-=x&-x) s+=BIT[x]; return s; } void ins(int x,int s) { for (;x<=200000;x+=x&-x) BIT[x]+=s; } int main() { ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0); int n; cin>>n; string s; cin>>s; s='#'+s; for(int i=1;i<=2*n;i++) V[s[i]].pb(i); for(int i='a';i<='z';i++) { for(int j=0;j<sz(V[i])/2;j++) side[V[i][j]]=1; for(int j=sz(V[i])/2;j<sz(V[i]);j++) side[V[i][j]]=2; } ll ans=0,cnt=0; for(int i=1;i<=2*n;i++) { if(side[i]==2) { cnt++; p[i]=cnt; } else ans+=cnt; } for(int i='a';i<='z';i++) { for(int j=0;j<sz(V[i])/2;j++) p[V[i][j]]=p[V[i][j+sz(V[i])/2]]; } for(int i=1;i<=2*n;i++) { if(side[i]==2) continue; ans+=(ll)que(n)-que(p[i]); ins(p[i],1); } cout<<ans; return 0; }

Main.cpp: In function 'int main()':
Main.cpp:43:35: warning: array subscript has type 'char' [-Wchar-subscripts]
   43 |     for(int i=1;i<=2*n;i++) V[s[i]].pb(i);
      |                                   ^