CodeSignal Technical Assessment Bit Manipulation and Mathematical Reasoning

Question 1

What does the expression `n & (n-1)` evaluate to when n is a power of 2?

Accepted Answer

0

Answer

A power of 2 has exactly one set bit; subtracting 1 flips all lower bits, so ANDing gives 0.

Question 2

How do you check if the k-th bit (0-indexed) of integer n is set?

Accepted Answer

n & (1 << k)

Answer

Shifting 1 left by k positions creates a mask; ANDing with n isolates that bit, giving a non-zero result if it is set.

Question 3

What is 5 XOR 3 in decimal?

Accepted Answer

6

Answer

5 is 101 and 3 is 011 in binary; XOR gives 110, which equals 6 in decimal.

Question 4

What does left-shifting an integer n by 1 position (`n << 1`) effectively compute?

Accepted Answer

n * 2

Answer

Left-shifting by 1 appends a zero bit on the right, which doubles the value in base-2 representation.

Question 5

Which bit trick isolates the lowest set bit of integer n?

Accepted Answer

n & (-n)

Answer

The two's complement of n (-n) flips all bits and adds 1, so n & (-n) keeps only the rightmost set bit.

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