Boyer–Moore Majority Vote: When to Use It

Start with the idea

A problem is a good match for Boyer–Moore Majority Vote when it asks for strict-majority detection with constant memory. Here the concrete task is: Return the strict majority value; the input guarantees that one exists. The visible input [2, 1, 2, 3, 2, 2, 4] is an example, not a definition of the whole problem. Ask what operations the solution must support and what the input guarantees. Ask whether one pass is enough, whether order matters, and whether a later query will need information you already discarded. The right choice follows from those guarantees, not from a familiar noun in the prompt.

The decisive invariant is: Cancel different values in pairs so a strict majority remains as the candidate. Try to say why it applies to the task without quoting the implementation. Which fact becomes known after one update, and which possible answers remain? A scan turns a sequence into a small piece of state. Say what the state means after the first i elements, before you describe a loop body. If that claim cannot be maintained on a legal input, the pattern is wrong or one of its preconditions is missing. A counterexample is more useful than a vague warning: change one property of the sample, trace the first two steps, and identify the exact claim that fails.

Compare costs before committing. The advertised bound is O(n) time · O(1) space; identify the operation responsible for it and the extra memory it needs.