LeetCode 191 ·
Easy
Number of 1 Bits
Count the set bits in an unsigned integer.
Try it
Step through the core mechanic. The simulator below runs the bit manipulation shape this problem is built on.
Walk the pattern
No dedicated step-through for this one yet. The shape is Bit manipulation — its pattern page has the interactive walkthrough, the reference implementation, and a five-problem progression that this problem sits inside.
The approach
Repeatedly clear the lowest set bit with n &= n−1 and count the iterations. This loops once per set bit rather than over all 32 positions.
| Aspect | Value |
|---|---|
| Pattern | Bit manipulation |
| Recognise it by | Population count. |
| Time complexity | O(set bits) |
| Space complexity | O(1) |
| Difficulty | Easy |
Who asks it
Companies known to ask this problem, from public LeetCode company-tag aggregations. A signal of where to expect it, not a guarantee.