/in/foo.c: In function 'main':
/in/foo.c:20:2: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
  for(i=1;i<=n-1;i++)
  ^~~
/in/foo.c:37:3: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'for'
   for(i=1;i<=n;i++)
   ^~~
/in/foo.c:29:11: warning: 'u' may be used uninitialized in this function [-Wmaybe-uninitialized]
    book[u]=1;//记录当前已知离第一个顶点最近的顶点 
    ~~~~~~~^~