foo.cc: In function ‘void bfs()’:
foo.cc:22:49: warning: suggest parentheses around ‘-’ inside ‘<<’ [-Wparentheses]
   22 |                                         k|=(1<<j-1);
      |                                                ~^~
foo.cc:24:50: warning: suggest parentheses around ‘-’ inside ‘<<’ [-Wparentheses]
   24 |                                         k&=~(1<<j-1);
      |                                                 ~^~

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