Submission #1299560

#	Time	Username	Problem	Language	Result	Execution time	Memory
1299560		Haanhtien	Aesthetic (NOI20_aesthetic)	C++17	100 / 100	567 ms	70328 KiB

Aesthetic

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

#define ll long long
#define FOR(i, a, b) for(int i=(a), _b=(b); i<=_b; i++)
#define FORD(i, a, b) for(int i=(a), _b=(b); i>=_b; i--)
#define BIT(i, j) ((i>>j)&1)
#define pb push_back
#define ii pair<ll, ll>
#define pii pair<ll, ii>
#define all(x) x.begin(), x.end()
#define fi first
#define se second

const ll inf = 1e18;
const ll mod = 1e9+7;
const ll N = 300005;
const ll M = 50005;

int n, m;
ll w[N];
vector<ii> adj[N];
priority_queue<ii, vector<ii>, greater<ii>> pq;
ll fs[N], ft[N], suf[N];
void dijkstra (int s, ll f[])
{
    fill (f + 1, f + n + 1, inf);
    f[s] = 0; 
    pq.push ({0, s});
    while (!pq.empty())
    {
        auto [du, u] = pq.top(); pq.pop();
        if (du != f[u]) continue;
            
        for (auto [v, id] : adj[u])
        {
            if (f[v] > f[u] + w[id])
            {
                f[v] = f[u] + w[id];
                pq.push ({f[v], v});
            }
        }
    }
}

int num[N], low[N], timeDfs, tin[N], tout[N];
vector<ii> g[N];


bool dfs (int u, int id, ll x)
{
    num[u] = low[u] = ++timeDfs;
    tin[u] = timeDfs;
    for (auto [v, vid] : g[u])
    {
        if (vid == id) continue;
        if (!num[v])
        {
            if (dfs (v, vid, x)) return true;
            low[u] = min (low[u], low[v]);
            if (low[v] == num[v] && tin[v] <= tin[n] && tout[v] >= tout[n])
            {
                if (w[vid] + fs[u] + ft[v] + suf[vid] > x && ft[u] + fs[v] + w[vid] + suf[vid] > x)
                    return true;
            }
        }
        else low[u] = min (low[u], num[v]);
    }
    tout[u] = timeDfs;
    return false;
}
int vis[N];
bool check (ll x)
{
    for (int i = 1; i <= n; i++)
    {
        g[i].clear();
        num[i] = low[i] = 0;
        tin[i] = tout[i] = 0;
    }
    timeDfs = 0;
    for (int i = 1; i <= m; i++) vis[i] = 0;
    for (int u = 1; u <= n; u++)
    {
        for (auto [v, id] : adj[u])
        {
            if (vis[id]) continue;
            vis[id] = 1;
            if (w[id] + fs[u] + ft[v] <= x || ft[u] + fs[v] + w[id] <= x) 
            {
                //cout << id << '\n';
                g[u].pb({v, id});
                g[v].pb({u, id});
            }
        }
    }
    return dfs (1, 0, x);

}
void solve()
{
    cin >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        int u, v;
        cin >> u >> v >> w[i];
        adj[u].pb({v, i});
        adj[v].pb({u, i});
    }
    dijkstra (1, fs);
    dijkstra (n, ft);

    for (int i = m; i >= 1; i--) suf[i] = max(suf[i + 1], w[i + 1]);
    ll l = fs[n], r = fs[n] + suf[1] - 1, ans = fs[n] - 1;

    while (l <= r)
    {
        ll mid = l + r >> 1;
        if (check(mid))
        {
            ans = mid;
            l = mid + 1;
        }
        else
        {
            r = mid - 1;
        }
    }

    cout << ans + 1;
}
int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0), cout.tie(0);
    #define task "beautiful"
    if(fopen(task".inp", "r"))
    {
        freopen(task".INP", "r", stdin);
        freopen(task".OUT", "w", stdout);
    }

    if(fopen("task.inp", "r"))
    {
        freopen("task.INP", "r", stdin);
        freopen("task.OUT", "w", stdout);
    }

    solve();
    return 0;
}

Compilation message (stderr)

Aesthetic.cpp: In function 'int main()':
Aesthetic.cpp:138:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  138 |         freopen(task".INP", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
Aesthetic.cpp:139:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  139 |         freopen(task".OUT", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
Aesthetic.cpp:144:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  144 |         freopen("task.INP", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
Aesthetic.cpp:145:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  145 |         freopen("task.OUT", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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