#include <bits/stdc++.h>
using namespace std;
template<class T, class U>
void ckmin(T &a, U b)
{
if (a > b) a = b;
}
template<class T, class U>
void ckmax(T &a, U b)
{
if (a < b) a = b;
}
#define MP make_pair
#define PB push_back
#define LB lower_bound
#define UB upper_bound
#define fi first
#define se second
#define SZ(x) ((int) (x).size())
#define ALL(x) (x).begin(), (x).end()
#define FOR(i, a, b) for (auto i = (a); i < (b); i++)
#define FORD(i, a, b) for (auto i = (a) - 1; i >= (b); i--)
const int MAXN = 3e5 + 13;
const long long LLINF = 3e18;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<pii> vpi;
typedef vector<pll> vpl;
typedef pair<pll, int> ppi;
int N, M, C, T;
vector<ppi> edge[MAXN];
ll dist[2][MAXN];
ll D;
int st[MAXN], ft[MAXN];
bitset<MAXN> seen;
vi bcc[MAXN];
vpi edges;
void dijkstra(int u)
{
bool b = (u > 0);
fill(dist[b], dist[b] + N + 1, LLINF);
dist[b][u] = 0;
priority_queue<pll, vector<pll>, greater<pll> > pq;
pq.push({0, u});
while(!pq.empty())
{
ll d = pq.top().fi; int u = pq.top().se; pq.pop();
if (d != dist[u]) continue;
for (auto e : edge[u])
{
int v = e.se; ll nd = d + e.fi.fi;
if (nd < dist[b][v])
{
dist[b][v] = nd;
pq.push({nd, v});
}
}
}
}
void dfs(int u, int p)
{
st[u] = T;
ft[u] = T;
T++;
seen[u] = true;
for (auto e : edge[u])
{
int v = e.se; ll d = e.fi.fi;
//if this is not on any shortest paths we just ignore it.
if (dist[0][u] + d + dist[1][v] >= D && dist[1][u] + d + dist[0][v] >= D) continue;
//oh no it is part of a path shorter than D so we legit care about it.
if (v == p) continue;
if (seen[v])
{
if (st[v] > st[u]) continue;
edges.PB({u, v});
ckmin(ft[u], st[v]);
continue;
}
edges.PB({u, v});
dfs(v, u);
ckmin(ft[u], ft[v]);
if (ft[v] >= st[u])
{
while(!edges.empty())
{
pii p = edges.back();
edges.pop_back();
bcc[C].PB(p.fi);
bcc[C].PB(p.se);
if (p == MP(u, v)) break;
}
C++;
}
}
}
bool check()
{
//can you make the dist >D?
//ans is YES if there's a bridge & this thing extends dist by more than D.
T = 0;
fill(st, st + N, 0);
fill(ft, ft + N, 0);
seen.reset();
FOR(i, 0, C) bcc[i].clear();
C = 0;
FOR(i, 0, N)
{
if (seen[i]) continue;
dfs(i, N);
}
set<pii> bridges;
FOR(i, 0, C)
{
sort(ALL(bcc[i]));
bcc[i].erase(unique(ALL(bcc[i])), bcc[i].end());
if (SZ(bcc[i]) == 2)
{
bridges.insert({bcc[i][0], bcc[i][1]});
}
}
FOR(u, 0, N)
{
for (auto e : edge[u])
{
int v = e.se; ll mx = e.fi.se;
if (bridges.find({u, v}) == bridges.end()) continue;
if (dist[0][u] + mx + dist[1][v] >= D && dist[1][u] + mx + dist[0][v] >= D) return true;
}
}
return false;
//now just check if there's something we can extend that is a bridge.
}
int32_t main()
{
cout << fixed << setprecision(12);
cerr << fixed << setprecision(4);
ios_base::sync_with_stdio(false); cin.tie(0);
cin >> N >> M;
vector<array<int, 3> > eds(M);
FOR(i, 0, M)
{
int a, b, w;
cin >> a >> b >> w; a--; b--;
if (a == b) continue;
eds.PB({a, b, w});
}
reverse(ALL(eds));
int mx = 0;
for (auto e : eds)
{
int a = e[0], b = e[1], w = e[2];
edge[a].PB({{w, w + mx}, b});
edge[b].PB({{w, w + mx}, a});
ckmax(mx, w);
}
dijkstra(0);
dijkstra(N - 1);
ll lo = dist[0][N - 1], hi = 2 * lo + 1;
while(hi > lo)
{
D = (hi + lo + 1) >> 1;
if (check()) lo = D;
else hi = D - 1;
}
cout << lo << '\n';
return 0;
}
Compilation message
Aesthetic.cpp: In function 'void dijkstra(int)':
Aesthetic.cpp:60:24: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
60 | if (d != dist[u]) continue;
| ^
