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IPv4 Iterators and CIDR
Build practical IPv4 primitives: forward/reverse iterators, CIDR range expansion, and (finally) covering N sequential IPs with minimum CIDR blocks. This tests bitwise thinking, boundary discipline, and writing clear stateful code.
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Bit Manipulation
Bit manipulation uses XOR, shifts, and masks to solve problems in O(1) space that would otherwise need hash maps. About 5 core tricks -- XOR for uniqueness, bit checks, Brian Kernighan's count -- cover 90% of interview bit problems.
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Talk through the problem while you code. Signed-in reps become prep memory for the next session.
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Desktop required
Sorry - mobile cannot run the editor and tests yet. Use the next step below or email yourself a link to continue on desktop.
Bit Manipulation gives you a useful next rep while you are still on your phone.