# # 【LeetCode】380. Insert Delete GetRandom O(1) 解题报告（Python）

## # 题目描述：

Design a data structure that supports all following operations in average `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();
``````

## # 解题方法

``````class RandomizedSet(object):

def __init__(self):
"""
"""
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.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]

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

``````class RandomizedSet(object):

def __init__(self):
"""
"""
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]

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

https://leetcode.com/problems/insert-delete-getrandom-o1/discuss/85397/Simple-solution-in-Python

## # 日期

2018 年 9 月 17 日 —— 早上很凉，夜里更凉