First Unique Number

https://leetcode.com/explore/featured/card/30-day-leetcoding-challenge/531/week-4/3313/

You have a queue of integers, you need to retrieve the first unique integer in the queue.

Implement the FirstUnique class:

• FirstUnique(int[] nums) Initializes the object with the numbers in the queue.

• int showFirstUnique() returns the value of the first unique integer of the queue, and returns -1 if there is no such integer.

• void add(int value) insert value to the queue.

Example 1:

Input: 
["FirstUnique","showFirstUnique","add","showFirstUnique","add","showFirstUnique","add","showFirstUnique"]
[[[2,3,5]],[],[5],[],[2],[],[3],[]]
Output: 
[null,2,null,2,null,3,null,-1]

Explanation: 
FirstUnique firstUnique = new FirstUnique([2,3,5]);
firstUnique.showFirstUnique(); // return 2
firstUnique.add(5);            // the queue is now [2,3,5,5]
firstUnique.showFirstUnique(); // return 2
firstUnique.add(2);            // the queue is now [2,3,5,5,2]
firstUnique.showFirstUnique(); // return 3
firstUnique.add(3);            // the queue is now [2,3,5,5,2,3]
firstUnique.showFirstUnique(); // return -1

Example 2:

Input: 
["FirstUnique","showFirstUnique","add","add","add","add","add","showFirstUnique"]
[[[7,7,7,7,7,7]],[],[7],[3],[3],[7],[17],[]]
Output: 
[null,-1,null,null,null,null,null,17]

Explanation: 
FirstUnique firstUnique = new FirstUnique([7,7,7,7,7,7]);
firstUnique.showFirstUnique(); // return -1
firstUnique.add(7);            // the queue is now [7,7,7,7,7,7,7]
firstUnique.add(3);            // the queue is now [7,7,7,7,7,7,7,3]
firstUnique.add(3);            // the queue is now [7,7,7,7,7,7,7,3,3]
firstUnique.add(7);            // the queue is now [7,7,7,7,7,7,7,3,3,7]
firstUnique.add(17);           // the queue is now [7,7,7,7,7,7,7,3,3,7,17]
firstUnique.showFirstUnique(); // return 17

Example 3:

Input: 
["FirstUnique","showFirstUnique","add","showFirstUnique"]
[[[809]],[],[809],[]]
Output: 
[null,809,null,-1]

Explanation: 
FirstUnique firstUnique = new FirstUnique([809]);
firstUnique.showFirstUnique(); // return 809
firstUnique.add(809);          // the queue is now [809,809]
firstUnique.showFirstUnique(); // return -1

Constraints:

• 1 <= nums.length <= 10^5

• 1 <= nums[i] <= 10^8

• 1 <= value <= 10^8

• At most 50000 calls will be made to showFirstUnique and add.

实现一种支持O(1)时间查询最早出现的独特元素的数据结构，能实时插入并且当插入的数据已出现过时，该元素将不再看作独特。O(1)时间查询 => Hash Map，O(1)找最早出现并且能O(1)删除 => Doubly Linked List + Hash Map。可以用Python带的OrderedHashMap实现。为了及时释放已不再是独特的元素node所占的内存，用单独一个hash set记录出现过的数据。

class FirstUnique:
    class Node:
        def __init__(self, value):
            self.pre = self.nxt = None
            self.v = value

    def __init__(self, nums: List[int]):
        self.s, self.d = set(), {}
        self.head, self.tail = FirstUnique.Node(-1), FirstUnique.Node(-1)
        self.head.nxt = self.tail
        self.tail.pre = self.head
        for i in nums:
            self.add(i)

    def showFirstUnique(self) -> int:
        return self.head.nxt.v

    def add(self, value: int) -> None:
        if value not in self.s:
            node = FirstUnique.Node(value)
            self.d[value] = node
            node.pre = self.tail.pre
            node.nxt = self.tail
            node.pre.nxt = node
            self.tail.pre = node
            self.s.add(value)
        elif value in self.d:
            node = self.d[value]
            node.nxt.pre = node.pre
            node.pre.nxt = node.nxt
            del self.d[value]

# Your FirstUnique object will be instantiated and called as such:
# obj = FirstUnique(nums)
# param_1 = obj.showFirstUnique()
# obj.add(value)