Submission #37201

#	Time	Username	Problem	Language	Result	Execution time	Memory
37201		aome	007 (CEOI14_007)	C++14	100 / 100	366 ms	19956 KiB

007

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

const int N = 200005;
const int INF = 1e9;

int n, m;
int p0, p1, a[2];
int dis[2][N];
int f[N], dis2[N];
bool lose[N];
vector<int> G[N];

void bfs(int t) {
	for (int i = 1; i <= n; ++i) dis[t][i] = INF;
	queue<int> qu; dis[t][a[t]] = 0, qu.push(a[t]);
	while (qu.size()) {
		int u = qu.front(); qu.pop();
		for (auto v : G[u]) {
			if (dis[t][v] == INF) {
				dis[t][v] = dis[t][u] + 1, qu.push(v);
			}
		}
	}
}

void dfs(int u) {
	f[u] = 1;
	for (auto v : G[u]) {
		if (dis[0][v] + 1 != dis[0][u] || dis[1][v] + 1 != dis[1][u]) continue;
		if (!f[v]) dfs(v); f[u] = max(f[u], f[v] + 1);
	}
}

int main() {
	ios::sync_with_stdio(false);
	cin >> n >> m;
	cin >> p0 >> p1 >> a[0] >> a[1];
	for (int i = 1; i <= m; ++i) {
		int u, v; cin >> u >> v;
		G[u].push_back(v), G[v].push_back(u);
	}
	bfs(0), bfs(1);
	for (int i = 1; i <= n; ++i) {
		if (dis[0][i] < dis[0][p0] || dis[1][i] < dis[1][p0]) lose[i] = 1;
	}
	if (dis[0][p0] == dis[1][p0]) {
		for (int i = 1; i <= n; ++i) {
			if (dis[0][i] == dis[0][p0] && dis[1][i] == dis[1][p0] && !f[i]) dfs(i);
		}	
		for (int i = 1; i <= n; ++i) {
			if (f[i] > f[p0]) lose[i] = 1;
		}
	}
	for (int i = 1; i <= n; ++i) dis2[i] = -1;
	queue<int> qu; dis2[p1] = 0, qu.push(p1);
	while (qu.size()) {
		int u = qu.front(); qu.pop(); 
		if (lose[u]) {
			cout << dis2[u] - 1; return 0;
		}
		for (auto v : G[u]) {
			if (dis2[v] == -1) {
				dis2[v] = dis2[u] + 1, qu.push(v);
			}
		}
	}
}

• Subtask 1: 30 / 30
• Subtask 2: 70 / 70