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Thaumasiotes wrote:

For those who were curious why these could both work, note that (A && B) || C differs from A && (B || C) in two cases: when A is false, C is true, and B is any value.

But in this case in particular, those differences would create a bug when A is false (the year is not divisible by 4) at the same time that C is true (the year is divisible by 400). Since that can't happen, the bug cannot occur.