Submission #171523

#	Time	Username	Problem	Language	Result	Execution time	Memory
171523		TadijaSebez	007 (CEOI14_007)	C++11	100 / 100	511 ms	39084 KiB

007

#include <bits/stdc++.h>
using namespace std;
#define pb push_back
const int N=200050;
vector<int> E[N];
void BFS(int x, int n, int d[], vector<int> p[])
{
	for(int i=1;i<=n;i++) d[i]=-1;
	queue<int> q;
	q.push(x);
	d[x]=0;
	while(q.size())
	{
		int u=q.front();
		q.pop();
		for(int v:E[u])
		{
			if(d[v]==-1)
			{
				d[v]=d[u]+1;
				q.push(v);
				p[v].pb(u);
			}
			else if(d[v]==d[u]+1) p[v].pb(u);
		}
	}
}
int ds[N],dd[N];
vector<int> ps[N],pd[N];
void DFS(int u, int mark, int w[], vector<int> p[])
{
	w[u]|=mark;
	for(int v:p[u]) if((w[v]&mark)==0) DFS(v,mark,w,p);
}
int sw[N],dw[N];
bool Check(int a, int b, int n)
{
	DFS(a,1,sw,ps);
	DFS(b,2,sw,ps);
	int mns=ds[a];
	for(int i=1;i<=n;i++) if(sw[i]==3) mns=min(mns,ds[a]-ds[i]);
	DFS(a,1,dw,pd);
	DFS(b,2,dw,pd);
	int mnd=dd[a];
	for(int i=1;i<=n;i++) if(dw[i]==3) mnd=min(mnd,dd[a]-dd[i]);
	//printf("%i %i\n",mns,mnd);
	return mns>mnd;
}
int main()
{
	int n,m,s,d,a,b;
	scanf("%i %i",&n,&m);
	scanf("%i %i %i %i",&s,&d,&a,&b);
	for(int i=1,u,v;i<=m;i++) scanf("%i %i",&u,&v),E[u].pb(v),E[v].pb(u);
	BFS(s,n,ds,ps);
	BFS(d,n,dd,pd);
	//printf("%i %i %i %i\n",ds[a],ds[b],dd[a],dd[b]);
	int ans=min(dd[a]-ds[a],dd[b]-ds[b]);
	ans=max(ans,-1);
	if(ans!=-1 && dd[a]==dd[b] && ds[a]==ds[b])
	{
		if(Check(a,b,n)) ans--;
	}
	printf("%i\n",ans);
	return 0;
}

Compilation message (stderr)

007.cpp: In function 'int main()':
007.cpp:52:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%i %i",&n,&m);
  ~~~~~^~~~~~~~~~~~~~~
007.cpp:53:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%i %i %i %i",&s,&d,&a,&b);
  ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~
007.cpp:54:59: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  for(int i=1,u,v;i<=m;i++) scanf("%i %i",&u,&v),E[u].pb(v),E[v].pb(u);
                            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~

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