Submission #857170

#	Time	Username	Problem	Language	Result	Execution time	Memory
857170		RiverFlow	Valley (BOI19_valley)	C++14	100 / 100	142 ms	46244 KiB

valley

#include <bits/stdc++.h>

#define nl "\n"
#define no "NO"
#define yes "YES"
#define fi first
#define se second
#define vec vector
#define task "main"
#define _mp make_pair
#define ii pair<int, int>
#define sz(x) (int)x.size()
#define all(x) x.begin(), x.end()
#define evoid(val) return void(std::cout << val)
#define FOR(i, a, b) for(int i = (a); i <= (b); ++i)
#define FOD(i, b, a) for(int i = (b); i >= (a); --i)
#define unq(x) sort(all(x)); x.resize(unique(all(x)) - x.begin())

using namespace std;

template<typename U, typename V> bool maxi(U &a, V b) {
    if (a < b) { a = b; return 1; } return 0;
}
template<typename U, typename V> bool mini(U &a, V b) {
    if (a > b) { a = b; return 1; } return 0;
}

const int N = (int)2e5 + 9;
const int mod = (int)1e9 + 7;

void prepare(); void main_code();

int main() {
    ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    if (fopen(task".inp", "r")) {
        freopen(task".inp", "r", stdin);
        freopen(task".out", "w", stdout);
    }
    const bool MULTITEST = 0; prepare();
    int num_test = 1; if (MULTITEST) cin >> num_test;
    while (num_test--) { main_code(); }
}

void prepare() {};

int n, s, q, e;

const int LG = 17;

int par[N][LG + 1], h[N];

long long dist[N];

int lca(int u, int v) {
    if (u == v) return u;
    if (h[u] < h[v]) swap(u, v);
    FOD(j, LG, 0) if (h[par[u][j]] >= h[v]) u = par[u][j];
    if (u == v) return u;
    FOD(j, LG, 0) if (par[u][j] != par[v][j])
        u = par[u][j], v = par[v][j];
    return par[u][0];
}

const long long INF = (long long)1e16;

bool shop[N];

long long cshop[N], jmp[N][LG + 1], val[N];

vector<pair<int, int>> g[N];

int _timer = 0, tin[N], tout[N];

void dfs(int u, int p) {
    cshop[u] = INF;
    if (shop[u]) cshop[u] = dist[u];
    for(int j = 1; j <= LG; ++j) {
        par[u][j] = par[ par[u][j - 1] ][j - 1];
    }
    tin[u] = ++_timer;
    for(auto j : g[u]) if (j.fi ^ p) {
        int v = j.fi;
        h[v] = h[u] + 1;
        par[v][0] = u;
        dist[v] = dist[u] + j.se;
        dfs(v, u);
        cshop[u] = min(cshop[u], cshop[v]);
    }
    tout[u] = ++_timer;
}

void dfs2(int u, int p) {
    val[u] = cshop[u] - 2LL * dist[u];
    if (cshop[u] == INF) val[u] = INF;
    jmp[u][0] = min(val[u], val[p]);
    for(int j = 1; j <= LG; ++j) {
        jmp[u][j] = min(jmp[u][j - 1], jmp[par[u][j - 1]][j - 1]);
    }
    for(auto j : g[u]) if (j.fi ^ p) {
        dfs2(j.fi, u);
    }
}

ii E[N];

long long jump(int u, int p) {
    long long res = INF;
    res = min(res, val[u]);
    for(int j = LG; j >= 0; --j) {
        if (h[ par[u][j] ] < h[p]) continue ;
        res = min(res, jmp[u][j]);
        u = par[u][j];
    }
    return res;
}

void main_code() {
    cin >> n >> s >> q >> e;
    for(int i = 1; i < n; ++i) {
        int u, v, w; cin >> u >> v >> w;
        g[u].emplace_back(v, w);
        g[v].emplace_back(u, w);
        E[i] = _mp(u, v);
    }
    for(int i = 1; i <= s; ++i) {
        int x; cin >> x; shop[x] = 1;
    }
    FOR(i, 0, n) FOR(j, 0, LG) jmp[i][j] = INF;
    h[0] = -1; val[0] = INF;
    dfs(e, 0); dfs2(e, 0);
    while (q--) {
        int i, r; cin >> i >> r;
        int u = E[i].fi, v = E[i].se;
        if (h[u] > h[v]) swap(u, v);
        if (tin[v] <= tin[r] and tout[r] <= tout[v]) {
            long long l = jump(r, v);
            if (l == INF) {
                cout << "oo\n";
            } else {
                cout << l + dist[r] << nl;
            }
        } else {
            cout << "escaped\n";
        }
    }
}


/*     Let the river flows naturally     */

Compilation message (stderr)

valley.cpp: In function 'int main()':
valley.cpp:36:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   36 |         freopen(task".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
valley.cpp:37:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   37 |         freopen(task".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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