Submission #261391

#	Time	Username	Problem	Language	Result	Execution time	Memory
261391		Nightlight	Aesthetic (NOI20_aesthetic)	C++14	0 / 100	605 ms	108288 KiB

Aesthetic

#include <cstdio>
#include <queue>
#include <cstring>
#define pii pair<long long, int>
using namespace std;
 
int N, M;
vector<pii> adj[300005];
priority_queue<pii, vector<pii>, greater<pii>> pq;
long long dist[2][300005];
int U[300005], V[300005];
bool can[300005], ada[300005];
long long W[300005], best[300005];
vector<pair<int, int>> adj2[300005];
int disc[300005], low[300005], waktu, need;
long long p1[300005], p2[300005], pp1[300005], pp2[300005];
bool ok;
 
void BFS(int id, int st) {
  memset(ada, 0, sizeof(ada));
  pq.emplace(0LL, st);
  dist[id][st] = 0;
  int u, v;
  long long len, w;
  while(!pq.empty()) {
    len = pq.top().first;
    if(len != dist[id][u]) {pq.pop(); continue;}
    u = pq.top().second;
    pq.pop();
    for(pii now : adj[u]) {
      v = now.second;
      w = now.first;
      if(dist[id][v] > len + w) {
        dist[id][v] = len + w;
        pq.emplace(dist[id][v], v);
      }
    }
  }
}
 
void DFS(int u, int p) {
  disc[u] = low[u] = ++waktu;
  int v, id;
  for(pair<int, int> now : adj2[u]) {
    id = now.second;
    if(ada[id] == 0) continue;
    v = now.first; 
    if(disc[v] <= need) {
      DFS(v, u);
      if(low[v] > disc[u] && can[id] && disc[N] >= disc[v] && disc[N] <= waktu) {
        ok = 1;
      }else if(low[u] > low[v]) low[u] = low[v];
    }else if(p != v && low[u] > disc[v]) {
      low[u] = disc[v];
    }
  }
}
 
bool check(long long now) {
  ok = 0;
  need = waktu;
  for(int i = 1; i <= M; i++) {
    if(p1[i] > now && p2[i] > now) ada[i] = 0;
    else ada[i] = 1;
    if(pp1[i] > now && pp2[i] > now) can[i] = 1;
    else can[i] = 0;
  }
  DFS(1, 0);
  if(disc[N] <= need) return 1;
  if(ok) return 1;
  return 0;
}
 
int main() {
  memset(dist, 0x3f3f3f3f, sizeof(dist));
  scanf("%d %d", &N, &M);
  int u, v;
  long long w;
  for(int i = 1; i <= M; i++) {
    scanf("%d %d %lld", &u, &v, &w);
    U[i] = u, V[i] = v, W[i] = w;
    adj[u].emplace_back(w, v);
    adj[v].emplace_back(w, u);
    adj2[u].emplace_back(v, i);
    adj2[v].emplace_back(u, i);
  }
  for(int i = M - 1; i > 0; i--) {
    best[i] = max(best[i + 1], W[i + 1]);
  }
  BFS(0, 1);
  BFS(1, N);
  for(int i = 1; i <= M; i++) {
    p1[i] = dist[0][U[i]] + W[i] + dist[1][V[i]];
    p2[i] = dist[0][V[i]] + W[i] + dist[1][U[i]];
    pp1[i] = dist[0][U[i]] + best[i] + W[i] + dist[1][V[i]];
    pp2[i] = dist[0][V[i]] + best[i] + W[i] + dist[1][U[i]];
  }
  long long l = dist[0][N], r = dist[0][N] + 1000000000, res = dist[0][N], mid;
  while(l <= r) {
    mid = (l + r) >> 1;
    if(check(mid)) {
      l = mid + 1;
      res = l;
    }else r = mid - 1;
  }
  printf("%lld\n", res);
}

Compilation message (stderr)

Aesthetic.cpp: In function 'int main()':
Aesthetic.cpp:76:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d %d", &N, &M);
   ~~~~~^~~~~~~~~~~~~~~~~
Aesthetic.cpp:80:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d %d %lld", &u, &v, &w);
     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
Aesthetic.cpp: In function 'void BFS(int, int)':
Aesthetic.cpp:27:25: warning: 'u' may be used uninitialized in this function [-Wmaybe-uninitialized]
     if(len != dist[id][u]) {pq.pop(); continue;}
               ~~~~~~~~~~^

• Subtask 1: 0 / 5
• Subtask 2: 0 / 8
• Subtask 3: 0 / 7
• Subtask 4: 0 / 15
• Subtask 5: 0 / 16
• Subtask 6: 0 / 22
• Subtask 7: 0 / 27