Majority Element (Boyer-Moore)

/*
 * Problem : Process an array.
 * Input   : n, then n integers.
 * Output  : The majority element.
 * Approach: Cancel different pairs.
 * Time    : O(n)
 * Space   : O(1)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
    // This method solves the task. It receives the input and returns the answer.
    static int solve(int[] a) {
        // Step 1: candidate is the current guess. votes says how sure we are.
        int candidate = 0;
        int votes = 0;

        for (int value : a) {
            // Step 2: When the votes are 0, take the current value as the new guess.
            if (votes == 0) {
                candidate = value;
            }

            // Step 3: The same value adds a vote. A different value removes one vote.
            votes += (value == candidate) ? 1 : -1;
        }

        // Step 4: A majority element always survives the cancelling.
        return candidate;
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int size = scanner.nextInt();
        int[] a = new int[size];
        for (int i = 0; i < size; i++) {
            a[i] = scanner.nextInt();
        }
        System.out.println(solve(a));
    }
}