2021全国高校计算机能力挑战赛（决赛）Java

import java.util.HashSet;
import java.util.linkedList;
import java.util.Scanner;
import java.util.Set;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        int m = scanner.nextInt();
        int res = solve(n, m);
        System.out.println(res);
    }

    public static int solve(int n, int m) {
        //特殊情况判断
        if (n == 1 && m == 1) return 0;
        if (n >= m) {
            return n - m;
        }
        linkedList queue = new linkedList<>();
        Set set = new HashSet<>();
        queue.offer(new int[]{n, 0});
        set.add(n);
        while (!queue.isEmpty()) {
            int[] cur = queue.poll();
            int num = cur[0];
            int step = cur[1];
            if (num == m) {
                return step;
            }
            if (!set.contains(num - 1)) {
                set.add(num - 1);
                queue.offer(new int[]{num - 1, step + 1});
            }
            if (num < m && !set.contains(num * 2)) {
                set.add(num * 2);
                queue.offer(new int[]{num * 2, step + 1});
            }
        }
        return -1;
    }
}