Submission #656123

#	Time	Username	Problem	Language	Result	Execution time	Memory
656123		600Mihnea	Necklace (Subtask 1-3) (BOI19_necklace1)	C++17	45 / 85	1593 ms	2528 KiB

necklace

bool home = 0;
bool verbose = 1;

#include <bits/stdc++.h>

using namespace std;

mt19937 rng(7777);

typedef long double ld;

const ld PI = 3.14159265358979323846264338327950288419716939937510582097494459230781640628620899862803482534211706798214808651328230664709384460955058223172535940812848111745028410270193852110555964462294895493038196442881097566593344612847564823378678316527120190914;
using cd = complex<ld>;


int getlog2(int x) {
  if (x == 1) return 0;
  assert(x >= 2);
  assert(x % 2 == 0);
  return 1 + getlog2(x / 2);
}

void fft(vector<cd>& a, bool inv) {
  int n = (int)a.size(), k = getlog2(n);

  assert((1 << k) == n);


  for (int i = 0; i < n; i++) {
    int j = 0;
    for (int bit = 0; bit < k; bit++) {
      if (i & (1 << bit)) {
        j += (1 << (k - 1 - bit));
      }
    }
    if (i < j) {

      swap(a[i], a[j]);
    }
  }

  for (int l = 2; l <= n; l *= 2) {
    ld ang = 2 * PI / (ld)l;
    if (inv) ang *= -1;
    cd mlt(cos(ang), sin(ang));
    for (int i = 0; i < n; i += l) {
      cd cur(1);
      for (int j = 0; j < l / 2; j++) {
        cd x = a[i + j];
        cd y = a[i + l / 2 + j] * cur;
        a[i + j] = x + y;
        a[i + l / 2 + j] = x - y;
        cur *= mlt;
      }
    }
  }

  if (inv) {
    for (auto& x : a) {
      x /= n;
    }
  }
}

vector<cd> conv_smart(vector<cd> x, vector<cd> y) {
  int n = 1;
  while (n <= (int)x.size() + (int)y.size()) n *= 2;

  x.resize(n, 0);
  y.resize(n, 0);

  vector<cd> a(x.begin(), x.end());
  vector<cd> b(y.begin(), y.end());

  fft(a, 0);
  fft(b, 0);

  for (int i = 0; i < n; i++) a[i] *= b[i];

  fft(a, 1);
  vector<cd> sol;

  for (int i = 0; i < n; i++) {
    sol.push_back(a[i]);
  }

  return sol;
}

ld values[26];

const ld eps = 1e-6;

vector<ld> place(string s, int len) {
  int n = (int) s.size();
  if (len > n) {
    return {};
  }
  ld ang = 2 * PI / len;
  cd c(cos(ang), sin(ang));
  vector<cd> cs(len);
  cs[0] = 1;
  for (int i = 1; i < len; i++) {
    cs[i] = cs[i - 1] * c;
  }
  vector<cd> a(n);
  for (int i = 0; i < n; i++) {
    a[i] = values[s[i] - 'a'];
  }
  vector<ld> sol(n - len + 1);
  vector<cd> lol = conv_smart(cs, a);
  for (int i = 0; i < n - len + 1; i++) {
    sol[i] = norm(lol[i + len - 1]);
  }
  return sol;
}

string s, t;


bool isok(int len) {
  vector<ld> norms_s = place(s, len);
  vector<ld> norms_t = place(t, len);
  int n = (int) norms_s.size();
  int m = (int) norms_t.size();
  sort(norms_s.begin(), norms_s.end());
  sort(norms_t.begin(), norms_t.end());
  int j = 0;
  for (int i = 0; i < n; i++) {
    while (j < m && norms_t[j] < norms_s[i]) {
      j++;
    }
    if (0 <= j && j < m && abs(norms_s[i] - norms_t[j]) < eps) {
      return 1;
    }
    if (0 <= j - 1 && j - 1 < m && abs(norms_s[i] - norms_t[j - 1]) < eps) {
      return 1;
    }
  }
  return 0;
}

void print(int len) {
  vector<ld> norms_s = place(s, len);
  vector<ld> norms_t = place(t, len);
  int n = (int) norms_s.size();
  int m = (int) norms_t.size();
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < m; j++) {
      if (abs(norms_s[i] - norms_t[j]) < eps) {
        cout << i << " " << j << "\n";
        exit(0);
      }
    }
  }
}

int main() {
  for (int x = 0; x < 26; x++) {
    values[x] = cos(rng()) * 10;
  }
  if (!home) {
    verbose = 0;
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
  }
  if (home) {
    verbose = 1;
    freopen ("___input___.txt", "r", stdin);
  }

  cin >> s >> t;
  int n = (int) s.size(), m = (int) t.size();
  int len = min(n, m);
  while (!isok(len)) {
    len--;
  }
  cout << len << "\n";
  print(len);
  return 0;
}

Compilation message (stderr)

necklace.cpp: In function 'int main()':
necklace.cpp:170:13: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  170 |     freopen ("___input___.txt", "r", stdin);
      |     ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 25 / 25
• Subtask 2: 20 / 20
• Subtask 3: 0 / 40