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

Here we can use HashSet and LinkedHashSet to get the first Unique number, HashSet can hold already visited elements and LinkedHashSet has unique numbers in sequence of occurance, If same element present in HashSet means we have multiple copy of it and can never be the answer, Hence remove it from the LinkedHashSet.

Code

Output

2 2 3 -1

We encourage you to write a comment if you have a better solution or having any doubt on the above topic.

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