1 #include <cstdio>
 2 #include <vector>
 3 #include <cstring>
 4
 5 using namespace std;
 6
 7 vector<int> path[100002];
 8 int pre[100002];
 9
10 int N, S;
11
12 void dfs(int start) {
13     int cnt = path[start].size();
14     for(int i = 0; i < cnt;i++) {
15         int p = path[start][i];
16         if(pre[p] == 0) {
17             pre[p] = start;
18             dfs(p);
19         }
20
21     }
22 }
23 int main(int argc, char const *argv[])
24 {
25     int M;
26     //freopen("input.txt","r",stdin);
27     scanf("%d",&M);
28     while(M--) {
29         memset(path, 0, sizeof(path));
30         memset(pre, 0, sizeof(pre));
31         scanf("%d %d",&N,&S);
32         for(int i = 0; i < N-1; i++) {
33             int x,y;
34             scanf("%d %d",&x,&y);
35             path[x].push_back(y);
36             path[y].push_back(x);
37         }
38         pre[S] = -1;
39         dfs(S);
40         printf("%d", pre[1]);
41         for(int i = 2; i <= N; i++) {
42             printf(" %d",pre[i]);
43         }
44         puts("");
45     }
46     return 0;
47 }

 1 #include <cstdio>
 2 #include <vector>
 3 #include <cstring>
 4 #include <queue>
 5 using namespace std;
 6
 7 vector<int> path[100002];
 8 int pre[100002];
 9 queue <int> que;
10 int N, S;
11
12 int main(int argc, char const *argv[])
13 {
14     int M;
15     //freopen("input.txt","r",stdin);
16     scanf("%d",&M);
17     while(M--) {
18         memset(path, 0, sizeof(path));
19         memset(pre, 0, sizeof(pre));
20         scanf("%d %d",&N,&S);
21         for(int i = 0; i < N-1; i++) {
22             int x,y;
23             scanf("%d %d",&x,&y);
24             path[x].push_back(y);
25             path[y].push_back(x);
26         }
27         pre[S] = -1;
28         que.push(S);
29
30         while(!que.empty()) {
31             int p0 = que.front();que.pop();
32             int cnt = path[p0].size();
33             for(int i = 0; i < cnt;i++) {
34                 int p = path[p0][i];
35                 if(pre[p] == 0) {
36                     pre[p] = p0;
37                     que.push(p);
38                 }
39             }
40         }
41         printf("%d", pre[1]);
42         for(int i = 2; i <= N; i++) {
43             printf(" %d",pre[i]);
44         }
45         puts("");
46     }
47     return 0;
48 }