Submission #513844

#	Time	Username	Problem	Language	Result	Execution time	Memory
513844		czhang2718	Monochrome Points (JOI20_monochrome)	C++17	0 / 100	1 ms	332 KiB

monochrome

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

const int N=400001;

int n;
string s;
int r[N], l[N];
int sum[4*N];

void upd(int i, int x, int lx, int rx){
  sum[x]++;
  if(rx-lx==1) return;
  int m=(lx+rx)/2;
  if(i<m) upd(i, 2*x+1, lx, m);
  else upd(i, 2*x+2, m, rx);
}

void upd(int i) { upd(i, 0, 0, 2*n+1); }

int get_sum(int l, int r, int x, int lx, int rx){
  if(lx>=r || rx<=l) return 0;
  if(lx>=l && rx<=r) return sum[x];
  int m=(lx+rx)/2;
  return get_sum(l, r, 2*x+1, lx, m)+get_sum(l, r, 2*x+2, m, rx);
}

int get_sum(int l, int r) { 
  if(r<=l) return 0;
  return get_sum(l, r, 0, 0, 2*n+1); 
}

int main(){
  cin.tie(0)->sync_with_stdio(0);

  cin >> n >> s;
  vector<int> white, black;
  for(int i=n; i<2*n; i++){
    if(s[i]=='W') white.push_back(i+1);
    else black.push_back(i+1);
  }
  int j=0, k=0;
  for(int i=0; i<n; i++){
    if(s[i]=='B') {
      l[white[j]]=i+1, r[i+1]=white[j];
      j++;
    }
    else{
      l[black[k]]=i+1, r[i+1]=black[k];
      k++;
    }
  }
  // for(int i=0; i<n; i++){
  //   cout << "r[" << i+1 << "] = " << r[i+1] << "\n";
  // }

  long long ans=0;
  for(int i=1; i<=2*n; i++){
    if(r[i]) continue;
    ans+=get_sum(l[i]+1, i);
    upd(l[i]);
  }
  cout << (long long)n*(n-1)/2-ans;
}

• Subtask 1: 0 / 4
• Subtask 2: 0 / 21
• Subtask 3: 0 / 10
• Subtask 4: 0 / 65