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  1. #include<bits/stdc++.h>
  2. using namespace std;
  3. int main(){
  4.         int n;
  5.         string s;
  6.         cin >> n;
  7.         cin >> s;
  8.         vector<pair<char, long long> > b;
  9.         b.push_back({'-', 0});
  10.         {
  11.         int cnt = 0;
  12.         for(int i = 0; i < n; i++){
  13.                 if(i != 0){
  14.                         if(s[i] != s[i - 1]){
  15.                         b.push_back({s[i - 1], cnt});
  16.                         cnt = 0;
  17.                         }
  18.                 }
  19.                 cnt++;
  20.         }
  21.         b.push_back({s[s.size() - 1], cnt});
  22.         }
  23.         n = b.size();
  24.         vector<long long> pref_sum(n + 1, 0);
  25.         vector<vector<long long> > pref_sum1(n + 1, vector<long long>(3, 0));
  26.         long long ans = 0;
  27.         vector<long long> lt(3, 0);
  28.         vector<long long> ass(3, -1);
  29.         for(int i = 1; i < n; i++){
  30.                 pref_sum[i] += pref_sum[i - 1];
  31.                 pref_sum1[i][i % 2] += pref_sum1[i - 1][i % 2];
  32.                 pref_sum1[i][(i + 1) % 2] = pref_sum1[i - 1][(i + 1) % 2];
  33.                 if(i >= 3){
  34.                         if(b[i].first == b[i - 2].first){
  35.                                 lt[i % 2] = i;
  36.                         }
  37.                 }
  38.                 if(i != 1){
  39.                         long long max_pos = 0;
  40.                         max_pos = max(max_pos, ass[(i + 1) % 2] - 1);
  41.                         max_pos = max(max_pos, lt[i % 2] - 1);
  42.                         //cout << i << " " << max_pos << " " << pref_sum[i] << " " << pref_sum1[i][i % 2] << " " << endl;
  43.                         if(max_pos >= 1){
  44.                                 ans += (b[i].second * (pref_sum[max_pos]));
  45.                                 ans += (b[i].second * (pref_sum1[i][(i + 1) % 2] - pref_sum1[max_pos][(i + 1) % 2]));
  46.                         }
  47.                         else{
  48.                                 ans += (b[i].second * pref_sum1[i][(i + 1) % 2]);
  49.                         }
  50.                 }
  51.                 if(b[i].second > 1){
  52.                         ass[i % 2] = i;
  53.                 }
  54.                 pref_sum[i] += b[i].second;
  55.                 pref_sum1[i][i % 2] += b[i].second;
  56.         }
  57.        /* for(int i = 1; i < n; i++){
  58.                 cout << pref_sum[i] << " ";
  59.         }
  60.         cout << endl;*/
  61.         cout << ans << endl;
  62. }
  63.  
Success #stdin #stdout 0.01s 5432KB
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https://ideone.com/cWBDYv
language:
C++14 (gcc 8.3)
created:
2 years ago
visibility:
public

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