LeetCode 1429. First Unique Number Solution in Java, C++, Python & Go | Explanation + Code

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

Solution 1

PythonJavaC++Go

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)(code-box)

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); */(code-box)

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); */(code-box)

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); */(code-box)

Solution 2

PythonJava

class FirstUnique: def __init__(self, nums: List[int]): self.cnt = Counter(nums) self.q = deque(nums) def showFirstUnique(self) -> int: while self.q and self.cnt[self.q[0]] != 1: self.q.popleft() return -1 if not self.q else self.q[0] def add(self, value: int) -> None: self.cnt[value] += 1 self.q.append(value) # Your FirstUnique object will be instantiated and called as such: # obj = FirstUnique(nums) # param_1 = obj.showFirstUnique() # obj.add(value)(code-box)

class FirstUnique { private Map<Integer, Integer> cnt = new HashMap<>(); private Deque<Integer> q = new ArrayDeque<>(); public FirstUnique(int[] nums) { for (int v : nums) { cnt.put(v, cnt.getOrDefault(v, 0) + 1); q.offer(v); } } public int showFirstUnique() { while (!q.isEmpty() && cnt.get(q.peekFirst()) != 1) { q.poll(); } return q.isEmpty() ? -1 : q.peekFirst(); } public void add(int value) { cnt.put(value, cnt.getOrDefault(value, 0) + 1); q.offer(value); } } /** * Your FirstUnique object will be instantiated and called as such: * FirstUnique obj = new FirstUnique(nums); * int param_1 = obj.showFirstUnique(); * obj.add(value); */(code-box)