Submission #659839

#	Time	Username	Problem	Language	Result	Execution time	Memory
659839		600Mihnea	Event Hopping (BOI22_events)	C++17	0 / 100	1 ms	212 KiB

events

bool home = 1;
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
const int N = (int) 1e5 + 7;
int n;
int q;

struct T {
  int l;
  int r;
  int init;
};

bool operator < (T a, T b) {
  if (a.r != b.r) {
    return a.r < b.r;
  } else {
    return a.l < b.l;
  }
}

T v[N];
int dp[N];
int nxt[N];
int ant[N];
int inv[N];

int cnt_rs_under(int limit) {
  int low = 1, high = n, cnt = 0;
  while (low <= high) {
    int mid = (low + high) / 2;
    if (v[mid].r <= limit) {
      cnt = mid;
      low = mid + 1;
    } else {
      high = mid - 1;
    }
  }
  return cnt;
}

int main() {
  if (!home) {
    ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
  } else {
    freopen("input.txt", "r", stdin);
  }

  cin >> n >> q;
  for (int i = 1; i <= n; i++) {
    cin >> v[i].l >> v[i].r;
    v[i].init = i;
  }
  sort(v + 1, v + n + 1);
  for (int i = 1; i <= n; i++) {
    int x = cnt_rs_under(v[i].l - 1) + 1;
    int y = cnt_rs_under(v[i].r);
    for (int j = 1; j <= n; j++) {
      assert((v[i].l <= v[j].r && v[j].r <= v[i].r) == (x <= j && j <= y));
    }
  }
  for (int i = 1; i <= n; i++) {
    inv[v[i].init] = i;
  }
  for (int i = 1; i <= n; i++) {
    nxt[i] = -1;
    for (int j = 1; j <= n; j++) {
      if (v[j].l <= v[i].r) {
        if (nxt[i] == -1) {
          nxt[i] = j;
        } else {
          if (v[j].r > v[nxt[i]].r) {
            nxt[i] = j;
          }
        }
      }
    }
    if (nxt[i] != -1 && v[i].r >= v[nxt[i]].r) {
      nxt[i] = -1;
    }
  }
  for (int i = 1; i <= n; i++) {
    ant[i] = -1;
    for (int j = 1; j <= n; j++) {
      if (v[i].l <= v[j].r && v[j].r <= v[i].l) {
        if (ant[i] == -1) {
          ant[i] = j;
        }
      } else {
        if (v[j].l < v[ant[i]].l) {
          ant[i] = j;
        }
      }
    }
  }
  for (int iq = 1; iq <= q; iq++) {
    int ff, ss;
    cin >> ff >> ss;
    ff = inv[ff];
    ss = inv[ss];
    for (int i = 1; i <= n; i++) {
      dp[i] = -1;
    }
    int co = 0;
    while (nxt[ff] != -1 && v[nxt[ff]].r <= v[ss].l) {
      ff = nxt[ff];
      co++;
    }
    while (ant[ss] != -1 && v[ant[ss]].l >= v[ss].r) {
      ss = ant[ss];
      co++;
    }
    queue<int> q;
    q.push(ff);
    dp[ff] = 0;
    while (!q.empty()) {
      int a = q.front();
      q.pop();
      for (int b = 1; b <= n; b++) {
        if (v[b].l <= v[a].r && v[a].r <= v[b].r && dp[b] == -1) {
          dp[b] = 1 + dp[a];
          q.push(b);
        }
      }
    }
    if (dp[ss] == -1) {
      cout << "impossible\n";
      continue;
    }
    cout << co + dp[ss] << "\n";
  }

  return 0;
}
/**

**/

Compilation message (stderr)

events.cpp: In function 'int main()':
events.cpp:49:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   49 |     freopen("input.txt", "r", stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 10
• Subtask 2: 0 / 10
• Subtask 3: 0 / 15
• Subtask 4: 0 / 15
• Subtask 5: 0 / 20
• Subtask 6: 0 / 30