Submission #391961

#	Time	Username	Problem	Language	Result	Execution time	Memory
391961		8e7	007 (CEOI14_007)	C++14	0 / 100	248 ms	16368 KiB

007

//Challenge: Accepted
#include <iostream>
#include <algorithm>
#include <vector>
#include <utility>
#include <queue>
#define ll long long
#define maxn 200005
#define pii pair<int, int>
#define ff first
#define ss second
#define io ios_base::sync_with_stdio(0);
using namespace std;
//#include <bits/extc++.h>
//using namespace __gnu_pbds;
//template<class T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_upate>;

vector<int> adj[maxn];
int d1[maxn], d2[maxn], d3[maxn], d4[maxn];
bool found[maxn];

void bfs(int s, int dep[]) {
	queue<int> que;
	que.push(s);
	dep[s] = 0;
	while (que.size()) {
		int cur = que.front();
		que.pop();
		found[cur] = 1;
		for (int v:adj[cur]) {
			if (!found[v]) {
				found[v] = 1;
				dep[v] = dep[cur] + 1;
				que.push(v);
			}
		}
	}
}
int main() {
	io
	int n, m;
	cin >> n >> m;
	int pa, pb, st, st2;
	cin >> pa >> pb >> st >> st2;
	for (int i = 0;i < m;i++) {
		int u, v;
		cin >> u >> v;
		adj[u].push_back(v);
		adj[v].push_back(u);
	}
	int dis1 = 0, dis2 = 0;
	bfs(st, d1);
	dis1 = d1[pb] - d1[pa];
	int ans = 0;
	for (int i = 1;i <= n;i++) found[i] = 0;
	bfs(st2, d2);
	dis2 = d2[pb] - d2[pa];
	ans = min(dis1, dis2);
	//ans = min(ans, dep[pb] - dep[pa]);

	if (dis1 != dis2) cout << (ans > 0 ? ans : -1) << "\n";
	else {
		bfs(pa, d3);
		bfs(pb, d4);
		int ma = 0, mb = 0;
		for (int i = 1;i <= n;i++) {
			if (d3[i] + d1[i] == d1[pa] && d1[i] == d2[i]) { //if on shortest path
				ma = max(ma, d3[i]);
			}
			if (d4[i] + d2[i] == d1[pb] && d1[i] == d2[i]) { //if on shortest path
				mb = max(mb, d4[i]);
			}
		}
		if (ma < mb) ans--;
		cout << (ans > 0 ? ans : -1) << "\n";

	}
}
/*
6 6
1 2 3 4
1 5
5 6
6 3
6 4
1 2
3 4

7 8
1 7 4 5
4 5
1 2
1 3
2 4
3 5
4 6
5 6
6 7
 */

• Subtask 1: 0 / 30
• Subtask 2: 0 / 70