Common Bit Tricks

Here are bit manipulation patterns you will see repeatedly in interviews and production code.

$1.$ Check if $n$ is even: $n \& 1 = 0$.

$2.$ Set the $k$-th bit: $n | (1 << k)$.

$3.$ Clear the $k$-th bit: $n \& \sim(1 << k)$.

$4.$ Toggle the $k$-th bit: $n \wedge (1 << k)$.

$5.$ Check if $n$ is a power of 2: $n > 0$ and $n \& (n - 1) = 0$.

These tricks replace loops with single operations. Instead of checking divisibility by 2, you check the last bit. Instead of looping to set a bit, you use OR with a mask. Memorize these patterns.