Submission #521367

#	Time	Username	Problem	Language	Result	Execution time	Memory
521367		penguinhacker	Valley (BOI19_valley)	C++14	100 / 100	212 ms	42160 KiB

valley

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

#define ll long long
#define ar array

const int mxN=1e5;
const ll INF=1e18;
int n, ns, q, ed, tin[mxN], tout[mxN], t, anc[mxN][17];
ar<int, 3> edge[mxN];
vector<ar<int, 2>> adj[mxN];
ll d[mxN], dp[mxN], lft[mxN][17];
bool shop[mxN];

void dfs1(int u=ed) {
	tin[u]=t++;
	dp[u]=shop[u]?0:INF;
	for (int i=1; i<17; ++i)
		anc[u][i]=anc[u][i-1]^-1?anc[anc[u][i-1]][i-1]:-1;
	for (ar<int, 2> v : adj[u]) {
		anc[v[0]][0]=u;
		adj[v[0]].erase(find(adj[v[0]].begin(), adj[v[0]].end(), ar<int, 2>{u, v[1]}));
		d[v[0]]=d[u]+v[1];
		dfs1(v[0]);
		dp[u]=min(dp[u], dp[v[0]]+v[1]);
	}
	tout[u]=t++;
	lft[u][0]=dp[u]<INF?dp[u]-d[u]:INF;
}

bool ia(int u, int v) {
	return tin[u]<=tin[v]&&tout[v]<=tout[u];
}

void dfs2(int u=ed) {
	for (int i=1; i<17; ++i)
		lft[u][i]=min(lft[u][i-1], anc[u][i-1]^-1?lft[anc[u][i-1]][i-1]:INF);
	for (ar<int, 2> v : adj[u])
		dfs2(v[0]);
}

int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	cin >> n >> ns >> q >> ed, --ed;
	for (int i=1; i<n; ++i) {
		int u, v, w;
		cin >> u >> v >> w, --u, --v;
		edge[i]={u, v, w};
		adj[u].push_back({v, w});
		adj[v].push_back({u, w});
	}
	while(ns--) {
		int u;
		cin >> u, --u;
		shop[u]=1;
	}
	anc[ed][0]=-1;
	dfs1();
	dfs2();
	while(q--) {
		int I, u;
		cin >> I >> u, --u;
		int a=edge[I][0], b=edge[I][1];
		if (d[a]>d[b])
			swap(a, b);
		if (!ia(b, u)) {
			cout << "escaped\n";
		} else {
			int v=u;
			ll bst=INF;
			for (int i=16; ~i; --i)
				if (anc[v][i]^-1&&d[anc[v][i]]>=d[b]) {
					bst=min(bst, lft[v][i]);
					v=anc[v][i];
				}
			assert(v==b);
			ll ans=min(dp[u], d[u]+min(bst, lft[b][0]));
			if (ans==INF)
				cout << "oo\n";
			else
				cout << ans << "\n";
		}
	}
	return 0;
}

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