nyoj20_吝啬的国度_DFS

#include <iostream>
#include <cstdio>
#include <cstring>
#include <vector>

using namespace std;

vector<int> v[100005];
int pre[100005];

void dfs(int s){
    for(int i=0;i<v[s].size();i++){
        if(pre[v[s][i]]) continue;
        pre[v[s][i]]=s;
        dfs(v[s][i]);
    }
}

int main()
{
    int m;
    int n,s;
    int a,b;
    scanf("%d",&m);
    while(m--){
        memset(v,0,sizeof(v));
        memset(pre,0,sizeof(pre));
        scanf("%d %d",&n,&s);
        pre[s]=-1;
        for(int i=0;i<n-1;i++){
            scanf("%d %d",&a,&b);
            v[a].push_back(b);
            v[b].push_back(a);
        }
        dfs(s);
        for(int i=1;i<=n;i++){
            if(i<n){
                printf("%d ",pre[i]);
            }else{
                printf("%d\n",pre[i]);
            }
        }
    }
    return 0;
}