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

Solution 1

Python3JavaC++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)

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);
 */

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);
 */

Solution 2

Python3Java

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)

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);
 */

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