nyoj 20水

#include<stdio.h>
#include<string.h>
#define N 110000
struct node {
int u,v,next;
}bian[N*2];
int head[N],yong,pre[N];
void addedge(int u,int v) {
bian[yong].u=u;
bian[yong].v=v;
bian[yong].next=head[u];
head[u]=yong++;
}
int visit[N];
void dfs(int u) {
    visit[u]=1;
    int i;
    for(i=head[u];i!=-1;i=bian[i].next) {
        int v=bian[i].v;
        if(!visit[v]) {
            dfs(v);
          pre[v]=u;
        }
    }
    return ;
}
int main() {
     int t,n,s,i,j,k;
     scanf("%d",&t);
     while(t--) {
        scanf("%d%d",&n,&s);
        memset(head,-1,sizeof(head));
        yong=0;
        for(i=1;i<n;i++) {
            scanf("%d%d",&j,&k);
            addedge(j,k);
            addedge(k,j);
        }
        pre[s]=-1;
        memset(visit,0,sizeof(visit));
        dfs(s);
        for(i=1;i<n;i++)
            printf("%d ",pre[i]);
        printf("%d\n",pre[n]);
     }
return 0;
}