Submission #1175474

#	Time	Username	Problem	Language	Result	Execution time	Memory
1175474		CrabCNH	Valley (BOI19_valley)	C++20	100 / 100	130 ms	53756 KiB

valley

#include <bits/stdc++.h>

#define task   "BriantheCrab"

#define int    long long
#define pii    pair <int, int>
#define fi     first
#define se     second
#define szf    sizeof
#define sz(s)  (int)((s).size())

using namespace std;

template <class T> void mini (T &t, T f) {if (t > f) t = f;}
template <class T> void maxi (T &t, T f) {if (t < f) t = f;}

const int maxN = 1e5 + 5;
const int inf = 1e18 + 7;
const int mod = 1e9 + 7;
const int LOG = 21;

struct Ed {
    int u, v, w;
};

int n, s, q, e;
int timer = 0;
Ed edge[maxN];
int par[maxN], sz[maxN], head[maxN], in[maxN];
int d[maxN], h[maxN];
bool spe[maxN];
int dp[maxN], st[maxN][LOG], up[maxN][LOG];
vector <pii> adj[maxN];
 
void dfs (int u, int p) {
    sz[u] = 1;
    in[u] = ++ timer;
    for (auto [v, _] : adj[u]) {
        if (v != p) {
            par[v] = u;
            dfs (v, u);
            sz[u] += sz[v];
        }
    }
}
 
void HLD (int u, int p, int h) {
    head[u] = h;
    if (adj[u].size () == 1 && u != e) {
        return;
    }
    int nxt = 0, curmax = 0;
    for (auto [v, _] : adj[u]) {
        if (v == p) {
            continue;
        }
        if (sz[v] > curmax) {
            curmax = sz[v];
            nxt = v;
        }
    }
    HLD (nxt, u, h);
    for (auto [v, _] : adj[u]) {
        if (v != nxt && v != p) {
            HLD (v, u, v);
        }
    }
}
 
int LCA (int u, int v) {
    while (head[u] != head[v]) {
        if (sz[head[u]] < sz[head[v]]) {
            u = par[head[u]];
        }
        else {
            v = par[head[v]];
        }
    }
    return ((sz[u] > sz[v]) ? u : v);
}

void cal (int u, int p) {
    dp[u] = inf;
    //cout << u << '\n';
    if (spe[u]) {
        //cout << "hi\n";
        dp[u] = d[u];
    }
    for (auto [v, w] : adj[u]) {
        if (v == p) {
            continue;
        } 
        h[v] = h[u] + 1;
        d[v] = d[u] + w;
        //cout << v << ' ' <<u << '\n';
        cal (v, u);
        mini (dp[u], dp[v]);
    }
}

void solve () {
    cin >> n >> s >> q >> e;
    for (int i = 1; i < n; i ++) {
        int u, v, w;
        cin >> u >> v >> w;
        adj[u].push_back ({v, w});
        adj[v].push_back ({u, w});
        edge[i] = {u, v, w};
    }
    for (int i = 1; i <= s; i ++) {
        int x;
        cin >> x;
        spe[x] = 1;
    }
    dfs (e, e);
    HLD (e, e, e);
    cal (e, e);
    //cout << LCA (5, 1) << '\n';
    for (int i = 1; i <= n; i ++) {
        if (dp[i] != inf) {
            dp[i] -= 2 * d[i];
        }
    }
    for (int i = 1; i <= n; i ++) {
        st[i][0] = dp[par[i]];
        up[i][0] = par[i];
    }
    for (int j = 1; j < LOG; j ++) {
        for (int i = 1; i <= n; i ++) {
            up[i][j] = up[up[i][j - 1]][j - 1];
            st[i][j] = min (st[i][j - 1], st[up[i][j - 1]][j - 1]);
        }
    }
    // for (int i = 1; i <= n; i ++) {
        // cout << d[i] << '\n';
    // }
    while (q --) {
        int I, R;
        cin >> I >> R;
        auto [u, v, w] = edge[I];
        if (in[u] < in[v]) {
            swap (u, v);
        }
        v = R;
        //cout << u << ' ' << v << ' ' << LCA (u, v) << '\n';
        if (LCA (u, v) == u && h[u] <= h[v]) {
            if (spe[v] == true) {
                cout << "0\n";
            }
            //cout << dp[u] << ' ' << dp[v] << '\n';
            else if (dp[u] == inf) {
                cout << "oo\n";
            }
            else {
                int cur = h[v] - h[u];
                //cout << u << ' ' << v << ' ' << d[v] << '\n';
                int bestL = dp[v];
                int bestR = d[v];
                for (int i = 0; i < LOG; i ++) {
                    if ((cur >> i) & 1) {
                        mini (bestL, st[v][i]);
                        v = up[v][i];
                        //cout << v << ' ' << dp[v] << '\n';
                    }
                }
                if (bestL + bestR < 0) {
                    cout << "oo\n";
                    continue;
                }
                cout << bestL + bestR << '\n';
            }
        }
        else {
            cout << "escaped\n";
        }
    }
}

signed main () {
    cin.tie (nullptr) -> sync_with_stdio (false);
    if (fopen (task".inp", "r")) {
        freopen (task".inp", "r", stdin);
        freopen (task".out", "w", stdout);
    }
    int t = 1;
    //cin >> t;
    while (t --) {
        solve ();
    } 
    return 0;
}
// thfdgb

Compilation message (stderr)

valley.cpp: In function 'int main()':
valley.cpp:182:17: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  182 |         freopen (task".inp", "r", stdin);
      |         ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
valley.cpp:183:17: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  183 |         freopen (task".out", "w", stdout);
      |         ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 9 / 9
• Subtask 2: 27 / 27
• Subtask 3: 23 / 23
• Subtask 4: 41 / 41