#include <bits/stdc++.h>
using namespace std;
using ll = long long;
struct Fenwick {
vector<int> a;
int n{};
Fenwick() = default;
Fenwick(int n) : n(n), a(n + 1) {}
int sum(int i) {
int ans = 0;
for (int x = i + 1; x > 0; x -= x & -x) {
ans += a[x];
}
return ans;
}
void modify(int i, int val) {
for (int x = i + 1; x <= n; x += x & -x) {
a[x] += val;
}
}
};
ll intersecting(vector<int> &p) {
int n = p.size();
Fenwick fn(n);
ll ans = 0;
for (int i = 0; i < n; ++i) {
if (p[i] > i) {
ans -= fn.sum(i);
continue;
}
ans += fn.sum(p[i]);
fn.modify(p[i], 1);
}
return ans;
}
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int n;
cin >> n;
string s;
cin >> s;
vector<int> p(2 * n);
auto check_w = [&](int w) -> bool {
int b = n - w;
int left[2]{w, b}, pos[2]{};
bool yay = true;
for (int i = 0; i < 2 * n; ++i) {
int tp = s[i] == 'B';
if (left[tp]) {
pos[tp] += 1;
--left[tp];
} else {
if (pos[tp ^ 1] == 0 && tp == 1) {
return false;
}
pos[tp ^ 1] -= 1;
}
}
return true;
};
auto check_b = [&](int b) -> bool {
int w = n - b;
int left[2]{w, b}, pos[2]{};
bool yay = true;
for (int i = 0; i < 2 * n; ++i) {
int tp = s[i] == 'B';
if (left[tp]) {
pos[tp] += 1;
--left[tp];
} else {
if (pos[tp ^ 1] == 0 && tp == 0) {
return false;
}
pos[tp ^ 1] -= 1;
}
}
return true;
};
ll ans = 0;
auto calc = [&](int w) -> ll {
int b = n - w;
queue<int> pos[2];
int left[2]{w, b};
bool yay = true;
for (int i = 0; i < 2 * n; ++i) {
int tp = s[i] == 'B';
if (left[tp]) {
pos[tp].push(i);
--left[tp];
} else {
if (pos[tp ^ 1].empty()) {
yay = false;
break;
}
p[i] = pos[tp ^ 1].front();
p[p[i]] = i;
pos[tp ^ 1].pop();
}
}
if (yay) {
ll now = intersecting(p);
ans = max(ans, now);
return now;
} else {
return -1;
}
};
int lo = 0, hi = n + 1;
while (lo + 1 < hi) {
int mid = (lo + hi) >> 1;
if (check_w(mid)) lo = mid;
else hi = mid;
}
int R = lo;
lo = 0, hi = n + 1;
while (lo + 1 < hi) {
int mid = (lo + hi) >> 1;
if (check_b(mid)) lo = mid;
else hi = mid;
}
int L = n - lo;
assert(L <= R);
lo = L - 1, hi = R;
while (lo + 1 < hi) {
int mid = (lo + hi) >> 1;
if (calc(mid) >= calc(mid + 1)) lo = mid;
else hi = mid;
}
calc(lo);
calc(hi);
calc(lo + 1);
calc(hi - 1);
cout << ans << '\n';
return 0;
}
Compilation message
monochrome.cpp: In constructor 'Fenwick::Fenwick(int)':
monochrome.cpp:8:9: warning: 'Fenwick::n' will be initialized after [-Wreorder]
8 | int n{};
| ^
monochrome.cpp:7:17: warning: 'std::vector<int> Fenwick::a' [-Wreorder]
7 | vector<int> a;
| ^
monochrome.cpp:12:5: warning: when initialized here [-Wreorder]
12 | Fenwick(int n) : n(n), a(n + 1) {}
| ^~~~~~~
monochrome.cpp: In lambda function:
monochrome.cpp:59:14: warning: unused variable 'yay' [-Wunused-variable]
59 | bool yay = true;
| ^~~
monochrome.cpp: In lambda function:
monochrome.cpp:79:14: warning: unused variable 'yay' [-Wunused-variable]
79 | bool yay = true;
| ^~~
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
0 ms |
212 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
0 ms |
212 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
0 ms |
212 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
0 ms |
212 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
