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content: check if a number is a power of 2 (#196)

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* Check if a number is a power of 2

This representation may be easier to understand for some people.
If a number is power of two then `AND` operation between the number and its complement will result into the same number.

* Update binary.md

Co-authored-by: Yangshun Tay <tay.yang.shun@gmail.com>
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@ -17,7 +17,7 @@ Some helpful utility snippets:
- Set k<sup>th</sup> bit: `num |= (1 << k)`. - Set k<sup>th</sup> bit: `num |= (1 << k)`.
- Turn off k<sup>th</sup> bit: `num &= ~(1 << k)`. - Turn off k<sup>th</sup> bit: `num &= ~(1 << k)`.
- Toggle the k<sup>th</sup> bit: `num ^= (1 << k)`. - Toggle the k<sup>th</sup> bit: `num ^= (1 << k)`.
- To check if a number is a power of 2, `num & num - 1 == 0`. - To check if a number is a power of 2, `(num & num - 1) == 0` or `(num & (-num)) == num`.
## Corner cases ## Corner cases