Boyer–Moore majority vote: what does it solve and what’s the core idea?

Answer

It finds the element that appears more than n/2 times (if it exists). The idea is to cancel pairs of different elements; the remaining candidate is the majority. It runs in O(n) time and O(1) space.

function majority(nums: number[]): number {
  let cand = 0;
  let count = 0;
  for (const x of nums) {
    if (count === 0) cand = x;
    count += x === cand ? 1 : -1;
  }
  return cand;
}