# Insert Delete GetRandom O(1)

Design a data structure that supports all following operations inaverage**O(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();
```

分析

用set

```
class RandomizedSet:

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.set = set()

    def insert(self, val):
        """
        Inserts a value to the self.set. Returns true if the self.set did not already contain the specified element.
        :type val: int
        :rtype: bool
        """
        if val in self.set:
            return False
        self.set.add(val)
        return True

    def remove(self, val):
        """
        Removes a value from the self.set. Returns true if the self.set contained the specified element.
        :type val: int
        :rtype: bool
        """
        if val not in self.set:
            return False
        self.set.remove(val)
        return True

    def getRandom(self):
        """
        Get a random element from the self.set.
        :rtype: int
        """
        x = random.randint(0,len(self.set)-1)
        return list(self.set)[x]
```


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