foo.cc: In function 'int main()':
foo.cc:26:22: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
   26 |         if(b[a[i]]!=i&&a[a[i]]!=i||a[b[i]]!=i&&b[b[i]]!=i)//判断是否可行,由于是个圈，可逆，所以两次判定
      |            ~~~~~~~~~~^~~~~~~~~~~~

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