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

Solution

A very interesting problem. Use Map to find the duplicate elements. Use Queue to process the input.

C# Program to understand better

public class FirstUnique { Queue<int> queue = new Queue<int>(); Dictionary<int,int> map = new Dictionary<int,int>(); public FirstUnique(int[] nums) { for(int i=0;i<nums.Length;i++){ Add(nums[i]); } } public int ShowFirstUnique() { while(queue.Count > 0 && map[queue.Peek()] > 1) queue.Dequeue(); if(queue.Count == 0) return -1; return queue.Peek(); } public void Add(int value) { if(map.ContainsKey(value)){ map[value]++; } else{ map.Add(value,1); queue.Enqueue(value); } } } /** * Your FirstUnique object will be instantiated and called as such: * FirstUnique obj = new FirstUnique(nums); * int param_1 = obj.ShowFirstUnique(); * obj.Add(value); */

Time Complexity:

For Add() – O(1) For Insertion – it takes O(n) For ShowFirstUnique, it takes O(logn)

Space Complexity: O(n)