双端队列，多写几遍，自然就会了

import java.util.*;
public class Solution {
    public ArrayList<Integer> maxInWindows(int [] num, int size) {
        if (size == 0 || num.length == 0) return new ArrayList<>();   
        ArrayList<Integer> list = new ArrayList<>();
        Deque<Integer> dp = new LinkedList<>();

        for (int i = 0; i < num.length; i ++ ) {
            while (!dp.isEmpty() && num[dp.getLast()] < num[i]) dp.pollLast();
            dp.offer(i);
            if (i - dp.getFirst() == size) dp.pollFirst();
            if (i - size >= -1) list.add(num[dp.getFirst()]); 
        }
        return list;
    }
}