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  wasif_shahzad  commented on Dec. 25, 2025, 6:08 a.m.

  can someone help me figure out what's wrong in this for SubTask 2 in Problem 3?

  void solve2() {
      int n;
      cin >> n;
      vector<int> a(n + 1, 1);
      for(int i = 1; i <= n; i++) {
          cin >> a[i];
      }
      auto cmp = [&] (auto x, auto y) -> bool {
          return x.second - x.first < y.second - y.first;
      };
      set<pair<int, int>, decltype(cmp)> breakable(cmp);
      set<pair<int, int>> single;
      vector<int> ans(n, -1);
      breakable.insert({0, n - 1});
      if(a[1] != 1) {
          cout << -1 << '\n';
          return;
      }
      int cur = 1;
      for(int i = 2; i <= n; i++) {
          if(a[i] > a[i - 1]) {
              // need to break
              while(cur < a[i]) {
                  if(breakable.empty()) {
                      cout << -1 << '\n';
                      return;
                  }
                  auto [l, r] = *breakable.begin();
                  breakable.erase(*breakable.begin());
                  int left = -1;
                  for(int j = l + 1; j <= r; j += 2) {
                      ans[j] = i - 1;
                      single.insert({j - 1, j - 1});
                      cur++;
                      if(cur == a[i]) {
                          left = j + 1;
                          break;
                      }
                  }
                  l = left;
                  if(r - l > 2) {
                      breakable.insert({l, r});
                  } else {
                      single.insert({l, r});
                  }
              }
          } else {
              // need to remove
              while(cur > a[i]) {
                  if(single.empty()) {
                      while(breakable.size()) {
                          auto [l, r] = *breakable.begin();
                          for(int j = l; j <= r; j++) {
                              ans[j] = i - 1;
                          }
                          breakable.erase(*breakable.begin());
                          cur--;
                          if(cur == a[i]) break;
                      }
                  } else if(single.size()) {
                      while(single.size()) {
                          auto [l, r] = *single.begin();
                          for(int j = l; j <= r; j++) {
                              ans[j] = i - 1;
                          }
                          single.erase(*single.begin());
                          cur--;
                          if(cur == a[i]) break;
                      }
                  } else break;
              }
              if(cur > a[i]) {
                  cout << -1 << '\n';
                  return;
              }
          }
      }
      for(int i = 0; i < n; i++) {
          if(ans[i] == -1) ans[i] = n;
      }
      for(int i = 0; i < n; i++) cout << ans[i] << " ";
      cout << "\n";
  }
  

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  thomas_li  commented on Dec. 25, 2025, 4:03 p.m.

  the answer

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  wasif_shahzad  commented on Dec. 25, 2025, 4:05 p.m.

  bruh. I meant what's the mistake :sob: