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1429. First Unique Number

Description

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.

Solutions

• Java
• C++
• Python
• Go

• class FirstUnique {
      private Map<Integer, Integer> cnt = new HashMap<>();
      private Set<Integer> unique = new LinkedHashSet<>();
  
      public FirstUnique(int[] nums) {
          for (int v : nums) {
              cnt.put(v, cnt.getOrDefault(v, 0) + 1);
          }
          for (int v : nums) {
              if (cnt.get(v) == 1) {
                  unique.add(v);
              }
          }
      }
  
      public int showFirstUnique() {
          return unique.isEmpty() ? -1 : unique.iterator().next();
      }
  
      public void add(int value) {
          cnt.put(value, cnt.getOrDefault(value, 0) + 1);
          if (cnt.get(value) == 1) {
              unique.add(value);
          } else {
              unique.remove(value);
          }
      }
  }
  
  /**
   * Your FirstUnique object will be instantiated and called as such:
   * FirstUnique obj = new FirstUnique(nums);
   * int param_1 = obj.showFirstUnique();
   * obj.add(value);
   */
  

• class FirstUnique {
  public:
      FirstUnique(vector<int>& nums) {
          for (int& v : nums) {
              ++cnt[v];
              q.push_back(v);
          }
      }
  
      int showFirstUnique() {
          while (q.size() && cnt[q.front()] != 1) q.pop_front();
          return q.size() ? q.front() : -1;
      }
  
      void add(int value) {
          ++cnt[value];
          q.push_back(value);
      }
  
  private:
      unordered_map<int, int> cnt;
      deque<int> q;
  };
  
  /**
   * Your FirstUnique object will be instantiated and called as such:
   * FirstUnique* obj = new FirstUnique(nums);
   * int param_1 = obj->showFirstUnique();
   * obj->add(value);
   */
  

• class FirstUnique:
      def __init__(self, nums: List[int]):
          self.cnt = Counter(nums)
          self.unique = OrderedDict({v: 1 for v in nums if self.cnt[v] == 1})
  
      def showFirstUnique(self) -> int:
          return -1 if not self.unique else next(v for v in self.unique.keys())
  
      def add(self, value: int) -> None:
          self.cnt[value] += 1
          if self.cnt[value] == 1:
              self.unique[value] = 1
          elif value in self.unique:
              self.unique.pop(value)
  
  
  # Your FirstUnique object will be instantiated and called as such:
  # obj = FirstUnique(nums)
  # param_1 = obj.showFirstUnique()
  # obj.add(value)
  
  

• type FirstUnique struct {
  	cnt map[int]int
  	q   []int
  }
  
  func Constructor(nums []int) FirstUnique {
  	cnt := map[int]int{}
  	for _, v := range nums {
  		cnt[v]++
  	}
  	return FirstUnique{cnt, nums}
  }
  
  func (this *FirstUnique) ShowFirstUnique() int {
  	for len(this.q) > 0 && this.cnt[this.q[0]] != 1 {
  		this.q = this.q[1:]
  	}
  	if len(this.q) > 0 {
  		return this.q[0]
  	}
  	return -1
  }
  
  func (this *FirstUnique) Add(value int) {
  	this.cnt[value]++
  	this.q = append(this.q, value)
  }
  
  /**
   * Your FirstUnique object will be instantiated and called as such:
   * obj := Constructor(nums);
   * param_1 := obj.ShowFirstUnique();
   * obj.Add(value);
   */
  

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