Reverse Bits
The problem
Reverse the order of all 32 bits in an unsigned 32-bit integer and return the resulting unsigned value. Leading zeros participate.
Example
1 → 2147483648 because the lowest bit moves to the highest position.
Need a hint?
Build the answer from the input’s least significant bit.
Write pseudocode, trace the example, or note an edge case. This scratchpad does not run code.
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Read the solution approach
Repeat exactly 32 times: shift the result left, append the input’s lowest bit, then shift the input right using unsigned semantics. Mask to 32 bits if the language uses unbounded integers. Convert a signed bitwise result to unsigned before returning.
Complexity
O(32), hence O(1), time and O(1) space.
Before moving on, explain why the algorithm is correct and trace a boundary case without looking at the approach.