Submission #298397

#	Time	Username	Problem	Language	Result	Execution time	Memory
298397		eriksuenderhauf	Monochrome Points (JOI20_monochrome)	C++17	35 / 100	2081 ms	8724 KiB

monochrome

#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("avx2")
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N = 2e5 + 5;
int a[4*N], nxt[3*N][2];

ll solve(int n, int i) {
  int ptr[2] = {i+n, i+n}, cnt[4] = {0, 0, 0, 0};
  ll val = 0;
  for (int j = i, c = a[i]; j < i+n; c = a[++j]) {
    cnt[c+2] += nxt[ptr[c]][c] - ptr[c];
    ptr[c] = nxt[ptr[c]][c] + 1;
    val += min(cnt[c+2], cnt[c^1]) + cnt[c]++;
  }
  return val;
}

int main() {
  ios_base::sync_with_stdio(false); cin.tie(0);
  auto cur_t = clock();
  int n; cin >> n;
  string s; cin >> s;
  for (int i = 0; i < 2*n; i++)
    a[i] = a[i+2*n] = s[i] == 'B';
  nxt[3*n][0] = nxt[3*n][1] = 3*n;
  for (int i = 3*n-1; i >= 0; i--) {
    nxt[i][0] = nxt[i+1][0], nxt[i][1] = nxt[i+1][1];
    nxt[i][a[i]^1] = i;
  }
  ll ans = 0;
  int i = 0;
  // for (int i = 1; i < n; i++)// if (s[i] != s[i+n])
  //   ans = max(ans, solve(n, i));
  while (i < n) {
    ans = max(ans, solve(n, i++));
    while (i < n && s[i-1] != s[i+n-1])
      i++;
  }
  cout << ans << "\n";
}

Compilation message (stderr)

monochrome.cpp: In function 'int main()':
monochrome.cpp:23:8: warning: unused variable 'cur_t' [-Wunused-variable]
   23 |   auto cur_t = clock();
      |        ^~~~~

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