Formatted question description: https://leetcode.ca/all/1429.html

1429. First Unique Number (Medium)

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 1.

// OJ: https://leetcode.com/problems/first-unique-number/

// Time:
//    FirstUnique: O(N)
//    showFirstUnique: O(1)
//    add: O(1)
// Space: O(N)
class FirstUnique {
    list<int> data;
    typedef list<int>::iterator iter;
    unordered_map<int, iter> m;
    unordered_set<int> s;
public:
    FirstUnique(vector<int>& nums) {
        for (int n : nums) add(n);
    }
    
    int showFirstUnique() {
        return data.size() ? data.front() : -1;
    }
    
    void add(int value) {
        if (s.count(value)) return;
        if (m.count(value)) {
            data.erase(m[value]);
            s.insert(value);
        } else {
            data.push_back(value);
            m[value] = prev(data.end());
        }
    }
};

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