Submission #604356

#	Time	Username	Problem	Language	Result	Execution time	Memory
604356		Plurm	Event Hopping (BOI22_events)	C++11	0 / 100	1589 ms	104756 KiB

events

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

vector<int> g[100005];
short dist[5005][5005];
short fastqueue[5000005];
short hidx = 0;
short tidx = 0;
int main() {
  memset(dist, 0x3F, sizeof(dist));
  int n, q;
  scanf("%d%d", &n, &q);
  vector<pair<int, int>> events;
  int k = sqrt(n);
  for (int i = 1; i <= n; i++) {
    int s, e;
    scanf("%d%d", &s, &e);
    events.push_back({s, e});
  }
  for (int i = 0; i < n; i++) {
    vector<int> tmp;
    for (int j = 0; j < n; j++) {
      if (i == j)
        continue;
      if (events[j].first <= events[i].second &&
          events[i].second <= events[j].second) {
        g[i].push_back(j);
      }
    }
  }
  for (int i = 0; i < n; i++) {
    dist[i][i] = 0;
    fastqueue[tidx++] = i;
    while (hidx != tidx) {
      int u = fastqueue[hidx++];
      for (int v : g[u]) {
        if (dist[i][v] > dist[i][u] + 1) {
          dist[i][v] = dist[i][u] + 1;
          fastqueue[tidx++] = v;
        }
      }
    }
  }
  for (int i = 0; i < q; i++) {
    int s, e;
    scanf("%d%d", &s, &e);
    if (dist[s - 1][e - 1] > n)
      printf("impossible\n");
    else
      printf("%hd\n", dist[s - 1][e - 1]);
    // can e be reached by s?, if yes, what is the shortest path?
  }
  return 0;
}

Compilation message (stderr)

events.cpp: In function 'int main()':
events.cpp:14:7: warning: unused variable 'k' [-Wunused-variable]
   14 |   int k = sqrt(n);
      |       ^
events.cpp:12:8: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   12 |   scanf("%d%d", &n, &q);
      |   ~~~~~^~~~~~~~~~~~~~~~
events.cpp:17:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   17 |     scanf("%d%d", &s, &e);
      |     ~~~~~^~~~~~~~~~~~~~~~
events.cpp:46:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   46 |     scanf("%d%d", &s, &e);
      |     ~~~~~^~~~~~~~~~~~~~~~

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