I should use more builtin functions. Thanks

can sb explain that how does it work??

^ is bitwise exclusive or

It compares corresponding bits in two numbers. It sets the corresponding bit in the output to 0 if the two corresponding input bits are the same and 1 if the bits are different.

See: https://wiki.python.org/moin/BitwiseOperators

what is this ^ symbol ?

Gorgeous, thank you

This is cute notation-wise, but certainly not "best practices", given that the more idiomatic knot-tying version uses O(1) memory, and this uses O(n).

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Yeah, I wrote a simple counter just to see if it would pass and it does. It doesn't care if you do weird things with mixing the brackets.

Obsolete