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Day 28 of 30 days Leetcode Challenge - First Unique Number

First Unique Number

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.

Solution

It's similar to LRU cache
Use a hash table and a Doubly Linked List

class FirstUnique {
    private var count = [Int: Int]()
    private var nodes = [Int: Node]()
    
    private var firstNode: Node?
    private var lastNode: Node?
    
    init(_ nums: [Int]) {
        for val in nums {
            add(val)
        }
    }
    
    func showFirstUnique() -> Int {
        if let node = firstNode {
            return node.val
        }
        return -1
    }
    
    func add(_ value: Int) {
        count[value] = (count[value] ?? 0) + 1
        
        if count[value] == 1 {
            var node = Node(value)
            lastNode?.next = node
            node.prev = lastNode
            lastNode = node
            
            if nodes.count == 0 {
                firstNode = node
            }
            
            nodes[value] = node
        }else{
            var node = nodes[value]
            
            if firstNode == node {
                firstNode = node?.next
            }
            
            if lastNode == node {
                lastNode = node?.prev
            }
            
            node?.prev?.next = node?.next
            node?.next?.prev = node?.prev
            
            nodes[value] = nil
        }
    }
}

class Node : Equatable {
    let val: Int
    var next: Node?
    var prev: Node?
    
    init(_ val: Int) {
        self.val = val
    }
    
    static func ==(lhs: Node, rhs: Node) -> Bool {
        return lhs.val == rhs.val
    }
}

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