foo.cc: In function 'void unique(node*)':
foo.cc:66:29: warning: variable 'pre2' set but not used [-Wunused-but-set-variable]
   66 |         node* pre = NULL, * pre2 = NULL,*i,*j;
      |                             ^~~~
foo.cc: In function 'int main()':
foo.cc:83:21: warning: unused variable 'i' [-Wunused-variable]
   83 |         int n1, n2, i, t;
      |                     ^
foo.cc:83:24: warning: unused variable 't' [-Wunused-variable]
   83 |         int n1, n2, i, t;
      |                        ^
foo.cc:85:31: warning: unused variable 'p' [-Wunused-variable]
   85 |         node* head1 = NULL, * p = NULL, * head2 = NULL;
      |                               ^

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