Leetcode - 1172 plate stack (Design - list + small top pile + stack))

List + Small cap pile + Stack （ Stack of double ended queue implementation ）

import java.util.*;

class DinnerPlates {
    
    //list  Stack   deque 
    // A queue that holds all subscripts that are not full 
    private PriorityQueue<Integer> deque;
    // Store all stacks in order 
    private List<Deque<Integer>> list;
    // Stack capacity 
    private int capacity;
    public DinnerPlates(int capacity) {
    
        this.capacity = capacity;
        // Subscripts are sorted from small to large 
        deque = new PriorityQueue<Integer>(new Comparator<Integer>(){
    
            public int compare(Integer i1,Integer i2){
    
                return i1.compareTo(i2);
            }
        });
        list= new ArrayList<>();
    }

    public void push(int val) {
    
        // If there is currently a stack that is not full 
         if(deque.size() > 0){
    
             // Take out the first stack that is not full from left to right 
             Deque<Integer> stack = list.get(deque.peek());
             // hold val Put in stack 
             stack.offerFirst(val);
             // If the stack is full 
             // Pop the stack from the never full stack queue 
             if(stack.size() == this.capacity)
                  deque.poll();
         }
         else{
    // The current stack is full 
             // Reopen a stack 
             Deque<Integer> stack = new LinkedList<>();
             // hold val Put in stack 
             stack.offerFirst(val);
             // Put the stack in the stack queue 
             list.add(stack);
             // If the stack is not full 
             if(stack.size() < this.capacity){
    
                 // Add the stack to the under stack queue 
                 deque.offer(list.size()-1);
             }
         }

    }

    public int pop() {
    
        // If there is no stack 
        if(list.size() == 0)
             return -1;
        int val = -1;
        int index = list.size()-1;
        // take list Delete the empty stack at the end 
        while(index >= 0 && list.get(index).size() == 0){
    
            list.remove(index);
            if(deque.contains(index))
                 deque.remove(index);
            index -= 1;
        }
        if(index >= 0 && list.get(index).size() > 0) {
    
             val = list.get(index).pollFirst();
            if(!deque.contains(index))
                deque.offer(index);
        }
        return val;
    }

    public int popAtStack(int index){
    
        if(index > list.size() -1)
            return -1;
        if(list.get(index).size() == 0)
            return -1;
        int val = list.get(index).pollFirst();
        if(!deque.contains(index))
            deque.offer(index);
        return val;
    }
}

/** * Your DinnerPlates object will be instantiated and called as such: * DinnerPlates obj = new DinnerPlates(capacity); * obj.push(val); * int param_2 = obj.pop(); * int param_3 = obj.popAtStack(index); */