Submission #874670

#	Time	Username	Problem	Language	Result	Execution time	Memory
874670		MilosMilutinovic	전압 (JOI14_voltage)	C++14	100 / 100	603 ms	56136 KiB

voltage

#include <bits/stdc++.h>
 
using namespace std;

struct op {
  int x;
  int y;
  int sx;
  int sy;
  int cx;
  int cy;
  bool b;
};
 
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, m;
  cin >> n >> m;
  vector<int> u(m), v(m);
  for (int i = 0; i < m; i++) {
    cin >> u[i] >> v[i];
    --u[i]; --v[i];
  }
  int ans = 0;
  bool bip = true;
  vector<int> f(n);
  vector<int> sz(n, 1);
  vector<int> col(n);
  iota(f.begin(), f.end(), 0);
  stack<op> stk;
  function<int(int)> Get = [&](int x) {
    return f[x] == x ? x : Get(f[x]);
  };
  function<int(int)> Col = [&](int x) {
    return f[x] == x ? col[x] : col[x] ^ Col(f[x]);
  };
  auto Unite = [&](int x, int y) {
    int px = Get(x);
    int py = Get(y);
    int cx = Col(x);
    int cy = Col(y);
    stk.push({px, py, sz[px], sz[py], col[px], col[py], bip});
    if (px == py) {
      if (cx == cy) {
        bip = false;
      }
      return;
    }
    if (sz[px] < sz[py]) {
      swap(px, py);
    }
    col[py] ^= col[px];
    if (cx == cy) {
      col[py] ^= 1;
    }
    f[py] = px;
    sz[px] += sz[py];
  };
  auto Rollback = [&]() {
    op o = stk.top();
    stk.pop();
    int x = o.x;
    int y = o.y;
    f[x] = x;
    f[y] = y;
    sz[x] = o.sx;
    sz[y] = o.sy;
    col[x] = o.cx;
    col[y] = o.cy;
    bip = o.b;
  };
  vector<vector<int>> qs(4 * m);
  function<void(int, int, int, int, int, int)> AddEdge = [&](int x, int l, int r, int ql, int qr, int i) {
    if (ql <= l && r <= qr) {
      qs[x].push_back(i);
      return;
    }
    int mid = (l + r) / 2;
    if (qr <= mid) {
      AddEdge(x << 1, l, mid, ql, qr, i);
    } else if (ql > mid) {
      AddEdge(x << 1 | 1, mid + 1, r, ql, qr, i);
    } else {
      AddEdge(x << 1, l, mid, ql, qr, i);
      AddEdge(x << 1 | 1, mid + 1, r, ql, qr, i);
    }
  };
  function<void(int, int, int)> Solve = [&](int x, int l, int r) {
    for (int i : qs[x]) {
      Unite(u[i], v[i]);
    }
    if (l == r) {
      if (bip && (Get(u[l]) != Get(v[l]) || Col(u[l]) == Col(v[l]))) {
        ans += 1;
      }
      for (int i : qs[x]) {
        Rollback();
      }
      return;
    }
    int mid = (l + r) / 2;
    Solve(x << 1, l, mid);
    Solve(x << 1 | 1, mid + 1, r);
    for (int i : qs[x]) {
      Rollback();
    }
  };
  for (int i = 0; i < m; i++) {
    if (i > 0) {
      AddEdge(1, 0, m - 1, 0, i - 1, i);
    }
    if (i + 1 < m) {
      AddEdge(1, 0, m - 1, i + 1, m - 1, i);
    }
  }
  Solve(1, 0, m - 1);
  cout << ans << '\n';
  return 0;
}

Compilation message (stderr)

voltage.cpp: In lambda function:
voltage.cpp:97:16: warning: unused variable 'i' [-Wunused-variable]
   97 |       for (int i : qs[x]) {
      |                ^
voltage.cpp:105:14: warning: unused variable 'i' [-Wunused-variable]
  105 |     for (int i : qs[x]) {
      |              ^

• Subtask 1: 10 / 10
• Subtask 2: 10 / 10
• Subtask 3: 35 / 35
• Subtask 4: 45 / 45