oj.uz

Submission #367655

# Submission time Handle Problem Language Result Execution time Memory
367655 2021-02-17T21:56:02 Z 534351 Aesthetic (NOI20_aesthetic) C++17
0 / 100
 2000 ms 101456 KB 
#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];
int parent[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[b][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 (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 the edge actually exists.
		if (v == p) continue;
		if (seen[v])
		{
			if (st[v] > st[u]) continue;
			edges.PB({u, v});
			ckmin(ft[u], st[v]);
			continue;
		}
        // cerr << u << ' ' << v << endl;
        // cerr << (bool) (dist[0][u] + d + dist[1][v] < D) << ' ' << (bool) (dist[1][u] + d + dist[0][v] < D) << endl;
		edges.PB({u, v});
        parent[v] = u;
		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;
        if (i == N - 1) return false;
        dfs(i, N);
    }
    set<pii> blocks;
    for (int i = N - 1; i != 0; i = parent[i])
    {
        blocks.insert({i, parent[i]});
        blocks.insert({parent[i], i});
    }
    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]});
            bridges.insert({bcc[i][1], bcc[i][0]});
        }
    }
    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 (blocks.find({u, v}) == blocks.end()) continue;
            // cerr << u << ' ' << v << ' ' << mx << ' ' << dist[0][u] + mx + dist[1][v] << ' ' << dist[1][u] + mx + dist[0][v] << endl;
            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;
    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 + 69;
    // cerr << mx << ' '<< lo << ' ' << hi << endl;
    while(hi > lo)
    {
        D = (hi + lo + 1) >> 1;
        if (check()) lo = D;
        else hi = D - 1;
    }
    cout << lo << '\n';
    return 0;
}

Subtask #1
0 / 5.0

# Verdict Execution time Memory Grader output
1 Correct 10 ms 14444 KB Output is correct
2 Incorrect 10 ms 14444 KB Output isn't correct
3 Halted 0 ms 0 KB -

Subtask #2
0 / 8.0

# Verdict Execution time Memory Grader output
1 Correct 10 ms 14444 KB Output is correct
2 Incorrect 10 ms 14444 KB Output isn't correct
3 Halted 0 ms 0 KB -

Subtask #3
0 / 7.0

# Verdict Execution time Memory Grader output
1 Execution timed out 2085 ms 57168 KB Time limit exceeded
2 Halted 0 ms 0 KB -

Subtask #4
0 / 15.0

# Verdict Execution time Memory Grader output
1 Execution timed out 2090 ms 72296 KB Time limit exceeded
2 Halted 0 ms 0 KB -

Subtask #5
0 / 16.0

# Verdict Execution time Memory Grader output
1 Correct 1316 ms 74192 KB Output is correct
2 Correct 775 ms 63440 KB Output is correct
3 Correct 914 ms 63708 KB Output is correct
4 Correct 905 ms 63696 KB Output is correct
5 Correct 903 ms 63952 KB Output is correct
6 Correct 921 ms 63904 KB Output is correct
7 Correct 910 ms 63952 KB Output is correct
8 Correct 916 ms 64080 KB Output is correct
9 Correct 894 ms 63800 KB Output is correct
10 Correct 919 ms 64336 KB Output is correct
11 Correct 1000 ms 63824 KB Output is correct
12 Correct 1127 ms 71504 KB Output is correct
13 Correct 930 ms 63952 KB Output is correct
14 Execution timed out 2005 ms 101456 KB Time limit exceeded
15 Halted 0 ms 0 KB -

Subtask #6
0 / 22.0

# Verdict Execution time Memory Grader output
1 Correct 1316 ms 74192 KB Output is correct
2 Correct 775 ms 63440 KB Output is correct
3 Correct 914 ms 63708 KB Output is correct
4 Correct 905 ms 63696 KB Output is correct
5 Correct 903 ms 63952 KB Output is correct
6 Correct 921 ms 63904 KB Output is correct
7 Correct 910 ms 63952 KB Output is correct
8 Correct 916 ms 64080 KB Output is correct
9 Correct 894 ms 63800 KB Output is correct
10 Correct 919 ms 64336 KB Output is correct
11 Correct 1000 ms 63824 KB Output is correct
12 Correct 1127 ms 71504 KB Output is correct
13 Correct 930 ms 63952 KB Output is correct
14 Execution timed out 2005 ms 101456 KB Time limit exceeded
15 Halted 0 ms 0 KB -

Subtask #7
0 / 27.0

# Verdict Execution time Memory Grader output
1 Correct 10 ms 14444 KB Output is correct
2 Incorrect 10 ms 14444 KB Output isn't correct
3 Halted 0 ms 0 KB -