(LeetCode) 380. Insert Delete GetRandom O(1)

380. Insert Delete GetRandom O(1)

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• 분류 : Design
• 난이도 : Medium

Problem

Implement the RandomizedSet class:

• RandomizedSet() Initializes the RandomizedSet object.
• bool insert(int val) Inserts an item val into the set if not present. Returns true if the item was not present, false otherwise.
• bool remove(int val) Removes an item val from the set if present. Returns true if the item was present, false otherwise.
• int getRandom() Returns a random element from the current set of elements (it’s guaranteed that at least one element exists when this method is called). Each element must have the same probability of being returned.

You must implement the functions of the class such that each function works in average O(1) time complexity.

Example 1

Input
["RandomizedSet", "insert", "remove", "insert", "getRandom", "remove", "insert", "getRandom"]
[[], [1], [2], [2], [], [1], [2], []]
Output
[null, true, false, true, 2, true, false, 2]

Explanation
RandomizedSet randomizedSet = new RandomizedSet();
randomizedSet.insert(1); // Inserts 1 to the set. Returns true as 1 was inserted successfully.
randomizedSet.remove(2); // Returns false as 2 does not exist in the set.
randomizedSet.insert(2); // Inserts 2 to the set, returns true. Set now contains [1,2].
randomizedSet.getRandom(); // getRandom() should return either 1 or 2 randomly.
randomizedSet.remove(1); // Removes 1 from the set, returns true. Set now contains [2].
randomizedSet.insert(2); // 2 was already in the set, so return false.
randomizedSet.getRandom(); // Since 2 is the only number in the set, getRandom() will always return 2.

Constraints

• -2^31 <= val <= 2^31 - 1
• At most 2 * 10^5 calls will be made to insert, remove, and getRandom.
• There will be at least one element in the data structure when getRandom is called.

Solution

Exapnder

class RandomizedSet() {

    /** Initialize your data structure here. */
    var set = mutableSetOf<Int>()

    /** Inserts a value to the set. Returns true if the set did not already contain the specified element. */
    fun insert(`val`: Int): Boolean = set.add(`val`)

    /** Removes a value from the set. Returns true if the set contained the specified element. */
    fun remove(`val`: Int): Boolean = set.remove(`val`)

    /** Get a random element from the set. */
    fun getRandom(): Int = set.elementAt(Random().nextInt(set.size))
}

/**
 * Your RandomizedSet object will be instantiated and called as such:
 * var obj = RandomizedSet()
 * var param_1 = obj.insert(`val`)
 * var param_2 = obj.remove(`val`)
 * var param_3 = obj.getRandom()
 */

Point of Thinking

• Set의 성질을 그대로 이용한다.
• getRandom() 메서드의 경우 set의 크기만큼 바운드값을 설정한다.
• 대응하는 인터페이스대로 처리하면 Accepted.