OJ-Problems-Source/QUSTOJ/1845_x7536110.cpp

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2016-10-12 11:26:41 +08:00
#include <iostream>
#include <cstring>
#include <cmath>
#include <climits>
#include <algorithm>
#include <cstdio>
#include <stdlib.h>
using namespace std;
#define MAXN 505
#define MAXM 500150
struct edges
{
int to;
int next;
}edge[MAXM];
int nx,ny,n,m,en,k;
int first[MAXN];
int cx[MAXN],cy[MAXN],distx[MAXN],disty[MAXN];
int que[MAXN],head,tail;
int ans;
int color[MAXN],cnt1,cnt2;
int w[550][550];
void init()
{
memset(cx,-1,sizeof(cx));
memset(cy,-1,sizeof(cy));
memset(first,-1,sizeof(first));
memset(w,0x3f3f3f3f,sizeof(w));
en=0;ans=0;
}
void add(int a, int b)
{
edge[en].to=b;
edge[en].next=first[a];
first[a]=en++;
}
bool bfs()
{
int i,j,k;
bool flag(0);
int h,t;
memset(distx,0,sizeof(distx));
memset(disty,0,sizeof(disty));
head=tail=0;
for(i=1;i<=nx;i++)
if (cx[i]==-1&&color[i]==1) que[tail++]=i;
while(head!=tail)
{
for(h=head,t=tail;h!=t;h=(h+1)%MAXN)
{
i=que[h];
if(color[i]!=1) continue;
for(k=first[i];k!=-1;k=edge[k].next)
{
j=edge[k].to;
if(color[j]!=-1) continue;
if(!disty[j])
{
disty[j]=distx[i]+1;
if (cy[j]==-1) flag=1;
else
{
distx[cy[j]]=disty[j]+1;
que[tail]=cy[j];
tail=(tail+1)%MAXN;
}
}
}
}
head=t;
}
return flag;
}
bool dfs(int i)
{
int j, k;
if(color[i]!=1) return 0;
for(k=first[i];k!=-1;k=edge[k].next)
{
j=edge[k].to;
if(color[j]!=-1) continue;
if(disty[j]==distx[i]+1)
{
disty[j]=0;
if(cy[j]==-1||dfs(cy[j]))
{
cx[i]=j,cy[j]=i;
return 1;
}
}
}
return 0;
}
int Hopcroft_Karp()
{
int i,j;
while(bfs())
for(i=1; i<=nx;i++)
if(color[i]==1&&cx[i]==-1&&dfs(i)) ans++;
return ans;
}
bool bipartite(int u,int c)
{
color[u]=c;
if(c==1) cnt1++;
else cnt2++;
for(int i=first[u];i!=-1;i=edge[i].next)
{
int v=edge[i].to;
if(color[v]==0)
{
if(!bipartite(v,-c))
return false;
}
else
if(color[v]==color[u])
return false;
}
return true;
}
void Floyd(int n)
{
for (int k=1;k<=n;k++)
{
for(int i=1;i<=n;i++)
for(int j=1;j<=n;j++)
if(w[i][j]>(w[i][k]+w[k][j]))
{
w[i][j]=w[i][k]+w[k][j];
}
}
}
int main(){
//freopen("indata","r",stdin);
//freopen("outdata","w",stdout);
int t;
int a,b,c;
scanf("%d",&t);
while(t--){
scanf("%d%d%d",&n,&m,&k);
init();
for(int i=1;i<=m;i++){
scanf("%d%d%d",&a,&b,&c);
w[a][b] = w[b][a] = c;
}
// printf("notdone\n");
Floyd(n);
//printf("fdone\n");
int knum = 0;
for(int i = 1;i <= n;i ++){
for(int j = 1;j <= n;j ++){
if(i == j) continue;
if(w[i][j] <= k) {
add(i,j);
knum ++;
}
}
}
knum/=2;
if(n == 0&& knum == 0){
printf("0\n");
continue;
}
memset(color,0,sizeof(color));
bool ok=1;
for(int i=1;i<=n;i++)
if(color[i]==0)
{
cnt1=cnt2=0;
if(!bipartite(i,1))
ok=0;
if(cnt1!=cnt2) ok=0;
}
if(!ok || n%2==1)
{
// printf("%d %d\n",ok,n%2 );
printf("Impossible\n");
continue;
}
nx=ny=n;
if(Hopcroft_Karp()!=n/2)
{
//printf("hk\n");
printf("Impossible\n");
continue;
}
printf("%d\n",ans);
for(int i=1;i<=n;i++)
{
if(i==1)
printf("%d",i);
else if(color[i]==color[1])
printf(" %d",i );
}
printf("\n");
}
return 0;
}