Create 1845_x7536110.cpp

QUSTOJ/1845_x7536110.cpp

@@ -0,0 +1,209 @@
+#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;
+}