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Submission #367662

# Submission time Handle Problem Language Result Execution time Memory
367662 2021-02-17T22:23:57 Z 534351 Aesthetic (NOI20_aesthetic) C++17
13 / 100
 2000 ms 47056 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], parent[MAXN], flagged[MAXN];
bitset<MAXN> seen;

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;
            ckmin(ft[u], st[v]);
            continue;
        }
        parent[v] = u;
        dfs(v, u);
        ckmin(ft[u], ft[v]);
        if (ft[v] > st[u])
        {
            flagged[v]++;
        }
    }
}

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(parent, parent + N, N);
    fill(st, st + N, 0);
    fill(ft, ft + N, 0);
    fill(flagged, flagged + N, 0);
    seen.reset();
    dfs(0, N);
    if (!seen[N - 1]) return false;
    for (int i = N - 1; i != 0; i = parent[i])
    {
        flagged[i]++;
    }
    FOR(u, 0, N)
    {
        for (auto e : edge[u])
        {
            int v = e.se; ll mx = e.fi.se;
            if (u != parent[v]) continue;
            if (flagged[v] != 2) 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 = 1e15;
    // 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
5.0 / 5.0

# Verdict Execution time Memory Grader output
1 Correct 6 ms 7404 KB Output is correct
2 Correct 5 ms 7404 KB Output is correct
3 Correct 5 ms 7404 KB Output is correct
4 Correct 5 ms 7404 KB Output is correct
5 Correct 6 ms 7404 KB Output is correct
6 Correct 5 ms 7404 KB Output is correct
7 Correct 5 ms 7404 KB Output is correct
8 Correct 6 ms 7404 KB Output is correct

Subtask #2
8.0 / 8.0

# Verdict Execution time Memory Grader output
1 Correct 6 ms 7404 KB Output is correct
2 Correct 5 ms 7404 KB Output is correct
3 Correct 5 ms 7404 KB Output is correct
4 Correct 5 ms 7404 KB Output is correct
5 Correct 6 ms 7404 KB Output is correct
6 Correct 5 ms 7404 KB Output is correct
7 Correct 5 ms 7404 KB Output is correct
8 Correct 6 ms 7404 KB Output is correct
9 Correct 9 ms 7788 KB Output is correct
10 Correct 9 ms 7660 KB Output is correct
11 Correct 9 ms 7660 KB Output is correct
12 Correct 9 ms 7680 KB Output is correct
13 Correct 8 ms 7660 KB Output is correct
14 Correct 8 ms 7660 KB Output is correct
15 Correct 8 ms 7660 KB Output is correct
16 Correct 9 ms 7660 KB Output is correct

Subtask #3
0 / 7.0

# Verdict Execution time Memory Grader output
1 Correct 1915 ms 39888 KB Output is correct
2 Correct 1827 ms 46800 KB Output is correct
3 Correct 1935 ms 46296 KB Output is correct
4 Correct 1923 ms 46348 KB Output is correct
5 Execution timed out 2011 ms 46544 KB Time limit exceeded
6 Halted 0 ms 0 KB -

Subtask #4
0 / 15.0

# Verdict Execution time Memory Grader output
1 Execution timed out 2033 ms 40656 KB Time limit exceeded
2 Halted 0 ms 0 KB -

Subtask #5
0 / 16.0

# Verdict Execution time Memory Grader output
1 Execution timed out 2089 ms 47056 KB Time limit exceeded
2 Halted 0 ms 0 KB -

Subtask #6
0 / 22.0

# Verdict Execution time Memory Grader output
1 Execution timed out 2089 ms 47056 KB Time limit exceeded
2 Halted 0 ms 0 KB -

Subtask #7
0 / 27.0

# Verdict Execution time Memory Grader output
1 Correct 6 ms 7404 KB Output is correct
2 Correct 5 ms 7404 KB Output is correct
3 Correct 5 ms 7404 KB Output is correct
4 Correct 5 ms 7404 KB Output is correct
5 Correct 6 ms 7404 KB Output is correct
6 Correct 5 ms 7404 KB Output is correct
7 Correct 5 ms 7404 KB Output is correct
8 Correct 6 ms 7404 KB Output is correct
9 Correct 9 ms 7788 KB Output is correct
10 Correct 9 ms 7660 KB Output is correct
11 Correct 9 ms 7660 KB Output is correct
12 Correct 9 ms 7680 KB Output is correct
13 Correct 8 ms 7660 KB Output is correct
14 Correct 8 ms 7660 KB Output is correct
15 Correct 8 ms 7660 KB Output is correct
16 Correct 9 ms 7660 KB Output is correct
17 Correct 1915 ms 39888 KB Output is correct
18 Correct 1827 ms 46800 KB Output is correct
19 Correct 1935 ms 46296 KB Output is correct
20 Correct 1923 ms 46348 KB Output is correct
21 Execution timed out 2011 ms 46544 KB Time limit exceeded
22 Halted 0 ms 0 KB -