Submission #518868

#	Time	Username	Problem	Language	Result	Execution time	Memory
518868		penguinhacker	Valley (BOI19_valley)	C++14	23 / 100	216 ms	63940 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, d1[mxN], tin[mxN], tout[mxN], t, anc[mxN][17];
ar<int, 3> edge[mxN];
vector<ar<int, 2>> adj[mxN];
ll d2[mxN], lft[mxN][17], up[mxN], lft2[mxN][17];
bool shop[mxN], has[mxN];
ar<ll, 2> dp[mxN][2];

void ins(int u, ar<ll, 2> x) {
	if (x[0]<dp[u][0][0]) {
		dp[u][1]=dp[u][0];
		dp[u][0]=x;
	} else if (x[0]<dp[u][1][0])
		dp[u][1]=x;
}

void dfs1(int u=0) {
	has[u]=u==ed;
	tin[u]=t++;
	dp[u][0]=dp[u][1]={INF, -1};
	if (shop[u])
		ins(u, {0, -1});
	for (int i=1; i<17; ++i)
		anc[u][i]=anc[anc[u][i-1]][i-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]}));
		d1[v[0]]=d1[u]+1;
		d2[v[0]]=d2[u]+v[1];
		dfs1(v[0]);
		has[u]|=has[v[0]];
		ins(u, {dp[v[0]][0][0]+v[1], v[0]});
	}
	tout[u]=t++;
}

void dfs2(int u=0) {
	lft[u][0]=dp[u][0][0]-d2[u];
	lft2[u][0]=shop[u]?d2[u]:INF;
	for (int i=1; i<17; ++i) {
		lft[u][i]=min(lft[u][i-1], lft[anc[u][i-1]][i-1]);
		lft2[u][i]=min(lft2[u][i-1], lft2[anc[u][i-1]][i-1]);
	}
	if (shop[u])
		up[u]=0;
	for (ar<int, 2> v : adj[u]) {
		up[v[0]]=min(up[u]+v[1], (dp[u][0][1]==v[0]?dp[u][1][0]:dp[u][0][0])+v[1]);
		dfs2(v[0]);
	}
}

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

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;
	}
	dfs1();
	up[0]=shop[0]?0:INF;
	dfs2();
	while(q--) {
		int I, u;
		cin >> I >> u, --u;
		int a=edge[I][0], b=edge[I][1];
		if (d1[a]>d1[b])
			swap(a, b);
		if (ia(b, u)&&has[b]||!ia(b, u)&&!has[b]) {
			cout << "escaped\n";
			continue;
		}
		if (ia(b, u)) {
			int v=u;
			ll bst=INF;
			for (int i=16; ~i; --i)
				if (d1[anc[v][i]]>=d1[b]) {
					bst=min(bst, lft[v][i]);
					v=anc[v][i];
				}
			assert(v==b);
			ll ans=min(dp[u][0][0], d2[u]+min(bst, lft[b][0]));
			if (ans>INF/2)
				cout << "oo\n";
			else
				cout << ans << "\n";
		} else {
			int v=u;
			ll ans=dp[u][0][0], bst=INF;
			for (int i=16; ~i; --i)
				if (!ia(anc[v][i], a)) {
					bst=min(bst, lft[v][i]);
					v=anc[v][i];
				}
			if (!ia(v, a)) {
				bst=min(bst, lft[v][0]);
				v=anc[v][0];
			}
			assert(ia(v, a));
			ans=min(ans, d2[u]+bst);
			ans=min(ans, d2[u]-d2[v]+up[v]);
			//cout << ans << "\n";
			bst=INF;
			for (int i=16; ~i; --i)
				if (d1[a]-(1<<i)>=d1[v]) {
					bst=min(bst, lft2[a][i]);
					a=anc[a][i];
				}
			ans=min(ans, d2[u]+min(bst, lft2[v][0])-2*d2[v]);
			if (ans>INF/2)
				cout << "oo\n";
			else
				cout << ans << "\n";
		}
	}
	return 0;
}

Compilation message (stderr)

valley.cpp: In function 'int main()':
valley.cpp:88:15: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
   88 |   if (ia(b, u)&&has[b]||!ia(b, u)&&!has[b]) {
      |       ~~~~~~~~^~~~~~~~

• Subtask 1: 0 / 9
• Subtask 2: 0 / 27
• Subtask 3: 23 / 23
• Subtask 4: 0 / 41