Submission #82732

#	Time	Username	Problem	Language	Result	Execution time	Memory
82732		IOrtroiii	007 (CEOI14_007)	C++14	100 / 100	393 ms	49688 KiB

007

#include <queue>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
 
const int N = 200005;
 
int n, m, s, d, a, b;
vector<int> g[N];
int fa[N], fb[N];
 
void bfs(int start, int f[]) {
	for (int i = 1; i <= n; ++i) f[i] = -1;
	f[start] = 0;
	queue <int> q; q.push(start);
 
	while(!q.empty()) {
		int u = q.front(); q.pop();
		for (int v : g[u]) if (f[v] == -1) {
			f[v] = f[u] + 1; q.push(v);
		}
	}
}
 
int maxdep(int start) {
	vector<int> d(n + 1, -1);
	queue <int> q; q.push(start); d[start] = 0;
	int ans = 0;
	while(!q.empty()) {
		int u = q.front(); q.pop();
		ans = max(ans, d[u]);
		for (int v : g[u]) if (fa[v] == fa[u] - 1 && fb[v] == fb[u] - 1 && d[v] == -1) {
			d[v] = d[u] + 1; q.push(v);
		}
	}
	return ans;
}
 
int main() {
	scanf("%d %d", &n, &m);
	scanf("%d %d %d %d", &s, &d, &a, &b);
	for (int i = 1; i <= m; ++i) {
		int u, v; scanf("%d %d", &u, &v);
		g[u].push_back(v); g[v].push_back(u);
	}
	bfs(a, fa);
	bfs(b, fb);
	int wa = fa[d] - fa[s];
	int wb = fb[d] - fb[s];
	if (wa != wb) {
		cout << max(min(wa, wb), -1) << '\n';
	} else {
		int maxs = maxdep(s), maxd = maxdep(d);
		cout << max(wa - (wa + maxs < maxd), -1) << '\n';
	}
}

Compilation message (stderr)

007.cpp: In function 'int main()':
007.cpp:42:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d %d", &n, &m);
  ~~~~~^~~~~~~~~~~~~~~~~
007.cpp:43:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d %d %d %d", &s, &d, &a, &b);
  ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
007.cpp:45:18: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   int u, v; scanf("%d %d", &u, &v);
             ~~~~~^~~~~~~~~~~~~~~~~

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