foo.cc: In function 'void unique(node*)':
foo.cc:71:29: warning: variable 'pre2' set but not used [-Wunused-but-set-variable]
   71 |         node* pre = NULL, * pre2 = NULL, * i, * j;
      |                             ^~~~
foo.cc: In function 'int main()':
foo.cc:146:25: warning: unused variable 'i' [-Wunused-variable]
  146 |         int n1, n2, n3, i, t;
      |                         ^
foo.cc:146:28: warning: unused variable 't' [-Wunused-variable]
  146 |         int n1, n2, n3, i, t;
      |                            ^

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