Minimum Cost Climbing Stairs

/*
 * Problem : Climb stairs cheaply.
 * Input   : n, then n costs.
 * Output  : Least total price.
 * Approach: Two variables.
 * 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 long solve(int[] a) {
        // Step 1: Keep only the best cost to stand on the last two steps. "second" is step i - 2, "first" is step i - 1.
        long second = a[0];
        long first = a[1];
        for (int i = 2; i < a.length; i++) {
            // Step 2: To stand on step i, pay a[i] and come from the cheaper of the last two steps.
            long current = a[i] + Math.min(first, second);
            second = first;
            first = current;
        }
        // Step 3: The top can be reached from either of the last two steps.
        return Math.min(first, second);
    }

    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));
    }
}