"""
Design a data structure that supports all following operations in average O(1) time.

insert(val): Inserts an item val to the set if not already present.
remove(val): Removes an item val from the set if present.
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 1 is the only number in the set, getRandom always return 1.
randomSet.getRandom();

"""
from random import randint

class RandomizedSet(object):

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.vals = list()
        self.locs = 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 in self.locs: # O(1)
            return False
        else:
            self.vals.append(val)  # O(1)
            self.locs[val] = len(self.vals) - 1  # O(1)
            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 in self.locs: # O(1)
            lastval = self.vals[-1] # O(1)
            if lastval != val:
                pos = self.locs[val] # O(1)
                self.vals[pos], self.vals[-1] = self.vals[-1], self.vals[pos] # O(1)
                self.locs[lastval] = pos # O(1)
            self.vals.pop(-1) # O(1)
            self.locs.pop(val) # O(1)
            return True
        else:
            return False

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


# Your RandomizedSet object will be instantiated and called as such:
obj = RandomizedSet()
print obj.insert(1)
print obj.remove(2)
print obj.insert(2)
print obj.vals

print obj.getRandom()
print obj.remove(1)
print obj.vals

print obj.vals
print obj.insert(2)
print obj.getRandom()

