[Swift]LeetCode380. 常数时间插入、删除和获取随机元素 | Insert Delete GetRandom O(1)

原文地址：https://www.cnblogs.com/strengthen/p/10281055.html 

Design a data structure that supports all following operations in averageO(1) time. 

1. insert(val): Inserts an item val to the set if not already present.
2. remove(val): Removes an item val from the set if present.
3. getRandom: Returns a random element from current set of elements. Each element must have the same probability of being returned. 

Example:

// Init an empty set.
RandomizedSet randomSet = new RandomizedSet();

// Inserts 1 to the set. Returns true as 1 was inserted successfully.
randomSet.insert(1);

// Returns false as 2 does not exist in the set.
randomSet.remove(2);

// Inserts 2 to the set, returns true. Set now contains [1,2].
randomSet.insert(2);

// getRandom should return either 1 or 2 randomly.
randomSet.getRandom();

// Removes 1 from the set, returns true. Set now contains [2].
randomSet.remove(1);

// 2 was already in the set, so return false.
randomSet.insert(2);

// Since 2 is the only number in the set, getRandom always return 2.
randomSet.getRandom();

---

设计一个支持在平均 时间复杂度 O(1) 下，执行以下操作的数据结构。

1. insert(val)：当元素 val 不存在时，向集合中插入该项。
2. remove(val)：元素 val 存在时，从集合中移除该项。
3. getRandom：随机返回现有集合中的一项。每个元素应该有相同的概率被返回。

示例 :

// 初始化一个空的集合。
RandomizedSet randomSet = new RandomizedSet();

// 向集合中插入 1 。返回 true 表示 1 被成功地插入。
randomSet.insert(1);

// 返回 false ，表示集合中不存在 2 。
randomSet.remove(2);

// 向集合中插入 2 。返回 true 。集合现在包含 [1,2] 。
randomSet.insert(2);

// getRandom 应随机返回 1 或 2 。
randomSet.getRandom();

// 从集合中移除 1 ，返回 true 。集合现在包含 [2] 。
randomSet.remove(1);

// 2 已在集合中，所以返回 false 。
randomSet.insert(2);

// 由于 2 是集合中唯一的数字，getRandom 总是返回 2 。
randomSet.getRandom();

---

260ms

class RandomizedSet {
    var dic : [Int:Int] // value - key
    var arr : [Int] //value
    /** Initialize your data structure here. */
    init() {
        arr = [Int]()
        dic = [Int:Int]()
    }
    
    /** Inserts a value to the set. Returns true if the set did not already contain the specified element. */
    func insert(_ val: Int) -> Bool {
        if dic[val] != nil { return false}
        arr.append(val)
        dic[val] = arr.count - 1
        return true
    }
    
    /** Removes a value from the set. Returns true if the set contained the specified element. */
    func remove(_ val: Int) -> Bool {
        if let preIndex = dic[val]{
            let lastIndex = arr.count - 1
            dic[val] = nil
            if lastIndex != preIndex {
                dic[arr[lastIndex]] = preIndex
                arr.swapAt(preIndex, lastIndex)
            }
            arr.removeLast()
        }else{
            return false
        }
        return true
        
    }
    
    /** Get a random element from the set. */
    func getRandom() -> Int {
        let i = Int.random(in: 0 ..< arr.count)
        return arr[i]
    }
}

/**
 * Your RandomizedSet object will be instantiated and called as such:
 * let obj = RandomizedSet()
 * let ret_1: Bool = obj.insert(val)
 * let ret_2: Bool = obj.remove(val)
 * let ret_3: Int = obj.getRandom()
 */

---

264ms

class RandomizedSet {
    var nums:[Int] = [Int]()
    var m:[Int:Int] = [Int:Int]()

    /** Initialize your data structure here. */
    init() {
        
    }
    
    /** Inserts a value to the set. Returns true if the set did not already contain the specified element. */
    func insert(_ val: Int) -> Bool {
        if m[val] != nil
        {
            return false
        }
        nums.append(val)
        m[val] = nums.count - 1
        return true
    }
    
    /** Removes a value from the set. Returns true if the set contained the specified element. */
    func remove(_ val: Int) -> Bool {
        if m[val] == nil
        {
            return false
        }
        var last = nums.last!
        m[last] = m[val]
        nums[m[val]!] = last                
        nums.removeLast()
        m[val] = nil
        return true      
    }
    
    /** Get a random element from the set. */
    func getRandom() -> Int {
        return nums[Int.random(in: 0..<nums.count)]      
    }
}

/**
 * Your RandomizedSet object will be instantiated and called as such:
 * let obj = RandomizedSet()
 * let ret_1: Bool = obj.insert(val)
 * let ret_2: Bool = obj.remove(val)
 * let ret_3: Int = obj.getRandom()
 */
 

---

312ms

class RandomizedSet {
    private var dict: [Int: Int]
    private var array: [Int]

    /** Initialize your data structure here. */
    init() {
        self.dict = [Int: Int]()
        self.array = [Int]()
    }

    /** Inserts a value to the set. Returns true if the set did not already contain the specified element. */
    func insert(_ val: Int) -> Bool {
        if let _ = dict[val] {
            return false
        } else {
            dict[val] = array.count
            array.append(val)
            return true
        }
    }

    /** Removes a value from the set. Returns true if the set contained the specified element. */
    func remove(_ val: Int) -> Bool {
        if let index = dict[val] {
            if index == array.count - 1 {
                array.removeLast()
            } else {
                let last = array.removeLast()
                array[index] = last
                dict[last] = index
            }
            dict[val] = nil
            return true
        } else {
            return false
        }
    }

    /** Get a random element from the set. */
    func getRandom() -> Int {
        return array.count == 0 ? -1 : array[Int.random(in: 0..<array.count)]
    }
}

/**
 * Your RandomizedSet object will be instantiated and called as such:
 * let obj = RandomizedSet()
 * let ret_1: Bool = obj.insert(val)
 * let ret_2: Bool = obj.remove(val)
 * let ret_3: Int = obj.getRandom()
 */