/in/foo.cc: In function 'void add(int, int)':
/in/foo.cc:8:40: error: 'cnt' was not declared in this scope
 {   e[++tol]=(node){y,head[x]};head[x]=cnt; }  
                                        ^~~
/in/foo.cc: At global scope:
/in/foo.cc:26:5: error: 'maxx' does not name a type
     maxx=max(maxx,f[x]+g[x]);  // 求树的直径-1 
     ^~~~
/in/foo.cc:27:1: error: expected declaration before '}' token
 }  
 ^