insert_delete_get_random_O_1.py

"""

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:

-231 <= val <= 231 - 1
At most 2 * 105 calls will be made to insert, remove, and getRandom.
There will be at least one element in the data structure when getRandom is called.

"""

# V0
# IDEA : SET
import random
class RandomizedSet(object):

    def __init__(self):
        self.set = set()
        self._len = 0

    def insert(self, val):
        if val in self.set:
            return False
        self.set.add(val)
        self._len += 1
        return True

    def remove(self, val):
        if val not in self.set:
            return False
        self.set.remove(val)
        self._len -= 1
        return True

    def getRandom(self):
        if self._len == 0:
            return []
        ### NOTE : we get idx via randint
        idx = random.randint(0, self._len - 1)
        ### NOTE : transform set to list, for getting element via idx
        return list(self.set)[idx]

# V0'
# IDEA : SET
import random
class RandomizedSet(object):

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.set = set()
        self.size = 0

    def insert(self, val):
        """
        Inserts a value to the set. Returns true if the set did not already contain the specified element.
        :type val: int
        :rtype: bool
        """
        if val not in self.set:
            self.set.add(val)
            self.size += 1
            return True
        return False

    def remove(self, val):
        """
        Removes a value from the set. Returns true if the set contained the specified element.
        :type val: int
        :rtype: bool
        """
        if val in self.set:
            self.set.remove(val)
            self.size -= 1
            return True
        return False

    def getRandom(self):
        """
        Get a random element from the set.
        :rtype: int
        """
        # Notice this
        ind = random.randint(0, self.size - 1)
        # we use `list(self.set)` transform set to list
        return list(self.set)[ind]

# V0'
# IDEA : LIST + DICT
class RandomizedSet(object):

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.nums, self.pos = list(), dict()

    def insert(self, val):
        """
        Inserts a value to the set. Returns true if the set did not already contain the specified element.
        :type val: int
        :rtype: bool
        """
        if val not in self.pos:
            self.nums.append(val)
            self.pos[val] = len(self.nums) - 1
            return True
        return False

    def remove(self, val):
        """
        Removes a value from the set. Returns true if the set contained the specified element.
        :type val: int
        :rtype: bool
        """
        if val in self.pos:
            ### NOTICE HERE 
            # IDEA : 
            # -> GET THE LAST IDX, ELEMENT IN THE LIST FIRST 
            # -> THEN SWAP LAST AND THE to-remove ELEMENT (val) 
            # -> SO ONCE REMOVE THE LAST ELEMENT IN THE LIST
            # -> WE CAN DO THE EXPECTED OP
            # -> UPDATE THE DICT ON ACCORDINGLY
            idx, last = self.pos[val], self.nums[-1]
            self.nums[idx] = last
            self.pos[last] = idx
            self.nums.pop()
            self.pos.pop(val, 0)
            return True
        return False

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

# V1
# https://blog.csdn.net/fuxuemingzhu/article/details/82732532
import random
class RandomizedSet(object):

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.set = set()
        self.size = 0

    def insert(self, val):
        """
        Inserts a value to the set. Returns true if the set did not already contain the specified element.
        :type val: int
        :rtype: bool
        """
        if val not in self.set:
            self.set.add(val)
            self.size += 1
            return True
        return False

    def remove(self, val):
        """
        Removes a value from the set. Returns true if the set contained the specified element.
        :type val: int
        :rtype: bool
        """
        if val in self.set:
            self.set.remove(val)
            self.size -= 1
            return True
        return False

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

### Test case 
r=RandomizedSet()
assert r.insert(1)==True
assert r.getRandom()==1
assert r.remove(1)==True
assert r.insert(2)==True
assert r.insert(3)==True
assert r.remove(100)==False

r=RandomizedSet()
assert r.remove(100)==False
assert r.insert(2)==True
assert r.remove(2)==True
assert r.remove(1)==False
assert r.insert(2)==True
assert r.insert(3)==True
assert r.getRandom() in [1,2,3]

# V1'
# https://blog.csdn.net/fuxuemingzhu/article/details/82732532
class RandomizedSet(object):

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.nums, self.pos = list(), dict()

    def insert(self, val):
        """
        Inserts a value to the set. Returns true if the set did not already contain the specified element.
        :type val: int
        :rtype: bool
        """
        if val not in self.pos:
            self.nums.append(val)
            self.pos[val] = len(self.nums) - 1
            return True
        return False

    def remove(self, val):
        """
        Removes a value from the set. Returns true if the set contained the specified element.
        :type val: int
        :rtype: bool
        """
        if val in self.pos:
            idx, last = self.pos[val], self.nums[-1]
            self.nums[idx] = last
            self.pos[last] = idx
            self.nums.pop()
            self.pos.pop(val, 0)
            return True
        return False

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

# V1''
# http://bookshadow.com/weblog/2016/08/04/leetcode-insert-delete-getrandom-o1/
import random
class RandomizedSet(object):

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.dataMap = {}
        self.dataList = []

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

    def remove(self, val):
        """
        Removes a value from the set. Returns true if the set contained the specified element.
        :type val: int
        :rtype: bool
        """
        if val not in self.dataMap:
            return False
        idx = self.dataMap[val]
        tail = self.dataList.pop()
        if idx < len(self.dataList):
            self.dataList[idx] = tail
            self.dataMap[tail] = idx
        del self.dataMap[val]
        return True

    def getRandom(self):
        """
        Get a random element from the set.
        :rtype: int
        """
        return random.choice(self.dataList)

# V1'''
# https://www.hrwhisper.me/leetcode-insert-delete-getrandom-o1/
import random
class RandomizedSet(object):

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.output = []
        self.index = {}
        

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

    def remove(self, val):
        """
        Removes a value from the set. Returns true if the set contained the specified element.
        :type val: int
        :rtype: bool
        """
        if val not in self.index:
            return False
        index = self.index[val]
        last=self.output[-1]
        self.index[last] = index
        self.output[index] = last
        self.output.pop()
        del self.index[val]
        return True
        

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

# V2