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‎Problemset/0381-Insert Delete GetRandom O(1) - Duplicates allowed/README.md

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# 381. Insert Delete GetRandom O(1) - Duplicates allowed
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`RandomizedCollection` is a data structure that contains a collection of numbers, possibly duplicates (i.e., a multiset). It should support inserting and removing specific elements and also reporting a random element.
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Implement the `RandomizedCollection` class:
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* `RandomizedCollection()` Initializes the empty `RandomizedCollection` object.
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* `bool insert(int val)` Inserts an item `val` into the multiset, even if the item is already present. Returns `true` if the item is not present, `false` otherwise.
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* `bool remove(int val)` Removes an item `val` from the multiset if present. Returns `true` if the item is present, `false` otherwise. Note that if `val` has multiple occurrences in the multiset, we only remove one of them.
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* `int getRandom()` Returns a random element from the current multiset of elements. The probability of each element being returned is **linearly related** to the number of the same values the multiset contains.
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You must implement the functions of the class such that each function works on **average** `O(1)` time complexity.
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**Note:** The test cases are generated such that `getRandom` will only be called if there is **at least one** item in the `RandomizedCollection`.
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#### Example 1:
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<pre>
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<strong>Input:</strong>
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["RandomizedCollection", "insert", "insert", "insert", "getRandom", "remove", "getRandom"]
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[[], [1], [1], [2], [], [1], []]
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<strong>Output:</strong>
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[null, true, false, true, 2, true, 1]
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<strong>Explanation:</strong>
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RandomizedCollection randomizedCollection = new RandomizedCollection();
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randomizedCollection.insert(1); // return true since the collection does not contain 1.
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// Inserts 1 into the collection.
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randomizedCollection.insert(1); // return false since the collection contains 1.
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// Inserts another 1 into the collection. Collection now contains [1,1].
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randomizedCollection.insert(2); // return true since the collection does not contain 2.
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// Inserts 2 into the collection. Collection now contains [1,1,2].
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randomizedCollection.getRandom(); // getRandom should:
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// - return 1 with probability 2/3, or
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// - return 2 with probability 1/3.
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randomizedCollection.remove(1); // return true since the collection contains 1.
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// Removes 1 from the collection. Collection now contains [1,2].
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randomizedCollection.getRandom(); // getRandom should return 1 or 2, both equally likely.
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</pre>
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#### Constraints:
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* <code>-2<sup>31</sup> <= val <= 2<sup>31</sup> - 1</code>
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* At most <code>2 * 10<sup>5</sup></code> calls **in total** will be made to `insert`, `remove`, and `getRandom`.
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* There will be **at least one** element in the data structure when `getRandom` is called.
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## Solutions (Python)
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### 1. Solution
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```Python
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import random
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class RandomizedCollection:
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def __init__(self):
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self.numlist = []
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self.numindices = {}
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def insert(self, val: int) -> bool:
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self.numlist.append(val)
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if val not in self.numindices:
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self.numindices[val] = set()
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self.numindices[val].add(len(self.numlist) - 1)
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return len(self.numindices[val]) == 1
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def remove(self, val: int) -> bool:
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if val not in self.numindices:
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return False
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i = self.numindices[val].pop()
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if len(self.numindices[val]) == 0:
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self.numindices.pop(val)
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if i == len(self.numlist) - 1:
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self.numlist.pop()
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else:
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self.numlist[i] = self.numlist.pop()
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self.numindices[self.numlist[i]].remove(len(self.numlist))
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self.numindices[self.numlist[i]].add(i)
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return True
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def getRandom(self) -> int:
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return random.choice(self.numlist)
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# Your RandomizedCollection object will be instantiated and called as such:
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# obj = RandomizedCollection()
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# param_1 = obj.insert(val)
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# param_2 = obj.remove(val)
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# param_3 = obj.getRandom()
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```

‎Problemset/0381-Insert Delete GetRandom O(1) - Duplicates allowed/README_CN.md

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# 381. O(1) 时间插入、删除和获取随机元素 - 允许重复
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`RandomizedCollection` 是一种包含数字集合(可能是重复的)的数据结构。它应该支持插入和删除特定元素，以及删除随机元素。
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实现 `RandomizedCollection` 类:
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* `RandomizedCollection()`初始化空的 `RandomizedCollection` 对象。
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* `bool insert(int val)` 将一个 `val` 项插入到集合中，即使该项已经存在。如果该项不存在，则返回 `true` ，否则返回 `false` 。
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* `bool remove(int val)` 如果存在，从集合中移除一个 `val` 项。如果该项存在，则返回 `true` ，否则返回 `false` 。注意，如果 `val` 在集合中出现多次，我们只删除其中一个。
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* `int getRandom()` 从当前的多个元素集合中返回一个随机元素。每个元素被返回的概率与集合中包含的相同值的数量 **线性相关** 。
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您必须实现类的函数，使每个函数的 **平均** 时间复杂度为 `O(1)` 。
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**注意：**生成测试用例时，只有在 `RandomizedCollection` 中 **至少有一项** 时，才会调用 `getRandom` 。
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#### 示例 1:
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<pre>
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<strong>输入:</strong>
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["RandomizedCollection", "insert", "insert", "insert", "getRandom", "remove", "getRandom"]
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[[], [1], [1], [2], [], [1], []]
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<strong>输出:</strong>
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[null, true, false, true, 2, true, 1]
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<strong>解释:</strong>
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RandomizedCollection collection = new RandomizedCollection();// 初始化一个空的集合。
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collection.insert(1); // 返回 true，因为集合不包含 1。
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// 将 1 插入到集合中。
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collection.insert(1); // 返回 false，因为集合包含 1。
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// 将另一个 1 插入到集合中。集合现在包含 [1,1]。
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collection.insert(2); // 返回 true，因为集合不包含 2。
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// 将 2 插入到集合中。集合现在包含 [1,1,2]。
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collection.getRandom(); // getRandom 应当:
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// 有 2/3 的概率返回 1,
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// 1/3 的概率返回 2。
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collection.remove(1); // 返回 true，因为集合包含 1。
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// 从集合中移除 1。集合现在包含 [1,2]。
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collection.getRandom(); // getRandom 应该返回 1 或 2，两者的可能性相同。
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</pre>
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#### 提示:
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* <code>-2<sup>31</sup> <= val <= 2<sup>31</sup> - 1</code>
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* `insert`, `remove` 和 `getRandom` 最多 **总共** 被调用 <code>2 * 10<sup>5</sup></code> 次
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* 当调用 `getRandom` 时，数据结构中 **至少有一个** 元素
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## 题解 (Python)
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### 1. 题解
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```Python
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import random
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class RandomizedCollection:
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def __init__(self):
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self.numlist = []
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self.numindices = {}
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def insert(self, val: int) -> bool:
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self.numlist.append(val)
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if val not in self.numindices:
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self.numindices[val] = set()
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self.numindices[val].add(len(self.numlist) - 1)
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return len(self.numindices[val]) == 1
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def remove(self, val: int) -> bool:
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if val not in self.numindices:
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return False
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i = self.numindices[val].pop()
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if len(self.numindices[val]) == 0:
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self.numindices.pop(val)
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if i == len(self.numlist) - 1:
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self.numlist.pop()
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else:
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self.numlist[i] = self.numlist.pop()
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self.numindices[self.numlist[i]].remove(len(self.numlist))
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self.numindices[self.numlist[i]].add(i)
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return True
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def getRandom(self) -> int:
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return random.choice(self.numlist)
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# Your RandomizedCollection object will be instantiated and called as such:
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# obj = RandomizedCollection()
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# param_1 = obj.insert(val)
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# param_2 = obj.remove(val)
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# param_3 = obj.getRandom()
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```

‎Problemset/0381-Insert Delete GetRandom O(1) - Duplicates allowed/Solution.py

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import random
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class RandomizedCollection:
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def __init__(self):
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self.numlist = []
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self.numindices = {}
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def insert(self, val: int) -> bool:
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self.numlist.append(val)
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if val not in self.numindices:
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self.numindices[val] = set()
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self.numindices[val].add(len(self.numlist) - 1)
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return len(self.numindices[val]) == 1
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def remove(self, val: int) -> bool:
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if val not in self.numindices:
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return False
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i = self.numindices[val].pop()
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if len(self.numindices[val]) == 0:
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self.numindices.pop(val)
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if i == len(self.numlist) - 1:
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self.numlist.pop()
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else:
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self.numlist[i] = self.numlist.pop()
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self.numindices[self.numlist[i]].remove(len(self.numlist))
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self.numindices[self.numlist[i]].add(i)
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return True
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def getRandom(self) -> int:
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return random.choice(self.numlist)
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# Your RandomizedCollection object will be instantiated and called as such:
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# obj = RandomizedCollection()
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# param_1 = obj.insert(val)
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# param_2 = obj.remove(val)
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# param_3 = obj.getRandom()

‎README.md

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[374][374l] |[Guess Number Higher or Lower][374] |![py]
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[375][375l] |[Guess Number Higher or Lower II][375] |![py]
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[380][380l] |[Insert Delete GetRandom O(1)][380] |![rs]
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[381][381l] |[Insert Delete GetRandom O(1) - Duplicates allowed][381] |![py]
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[382][382l] |[Linked List Random Node][382] |![py]
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[383][383l] |[Ransom Note][383] |![py]
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[384][384l] |[Shuffle an Array][384] |![rs]
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[374]:Problemset/0374-Guess%20Number%20Higher%20or%20Lower/README.md#374-guess-number-higher-or-lower
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[375]:Problemset/0375-Guess%20Number%20Higher%20or%20Lower%20II/README.md#375-guess-number-higher-or-lower-ii
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[380]:Problemset/0380-Insert%20Delete%20GetRandom%20O\(1\)/README.md#380-insert-delete-getrandom-o1
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[381]:Problemset/0381-Insert%20Delete%20GetRandom%20O(1)%20-%20Duplicates%20allowed/README.md#381-insert-delete-getrandom-o1-duplicates-allowed
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[382]:Problemset/0382-Linked%20List%20Random%20Node/README.md#382-linked-list-random-node
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[383]:Problemset/0383-Ransom%20Note/README.md#383-ransom-note
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[384]:Problemset/0384-Shuffle%20an%20Array/README.md#384-shuffle-an-array
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[374l]:https://leetcode.com/problems/guess-number-higher-or-lower/
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[375l]:https://leetcode.com/problems/guess-number-higher-or-lower-ii/
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[380l]:https://leetcode.com/problems/insert-delete-getrandom-o1/
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[381l]:https://leetcode.com/problems/insert-delete-getrandom-o1-duplicates-allowed/
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[382l]:https://leetcode.com/problems/linked-list-random-node/
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[383l]:https://leetcode.com/problems/ransom-note/
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[384l]:https://leetcode.com/problems/shuffle-an-array/

‎README_CN.md

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[374][374l] |[猜数字大小][374] |![py]
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[375][375l] |[猜数字大小 II][375] |![py]
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[380][380l] |[O(1) 时间插入、删除和获取随机元素][380] |![rs]
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[381][381l] |[O(1) 时间插入、删除和获取随机元素 - 允许重复][381] |![py]
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[382][382l] |[链表随机节点][382] |![py]
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[383][383l] |[赎金信][383] |![py]
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[384][384l] |[打乱数组][384] |![rs]
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[374]:Problemset/0374-Guess%20Number%20Higher%20or%20Lower/README_CN.md#374-猜数字大小
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[375]:Problemset/0375-Guess%20Number%20Higher%20or%20Lower%20II/README_CN.md#375-猜数字大小-ii
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[380]:Problemset/0380-Insert%20Delete%20GetRandom%20O\(1\)/README_CN.md#380-o1-时间插入删除和获取随机元素
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[381]:Problemset/0381-Insert%20Delete%20GetRandom%20O(1)%20-%20Duplicates%20allowed/README_CN.md#381-o1-时间插入、删除和获取随机元素---允许重复
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[382]:Problemset/0382-Linked%20List%20Random%20Node/README_CN.md#382-链表随机节点
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[383]:Problemset/0383-Ransom%20Note/README_CN.md#383-赎金信
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[384]:Problemset/0384-Shuffle%20an%20Array/README_CN.md#384-打乱数组
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[374l]:https://leetcode.cn/problems/guess-number-higher-or-lower/
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[375l]:https://leetcode.cn/problems/guess-number-higher-or-lower-ii/
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[380l]:https://leetcode.cn/problems/insert-delete-getrandom-o1/
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[381l]:https://leetcode.cn/problems/insert-delete-getrandom-o1-duplicates-allowed/
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[382l]:https://leetcode.cn/problems/linked-list-random-node/
34433446
[383l]:https://leetcode.cn/problems/ransom-note/
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[384l]:https://leetcode.cn/problems/shuffle-an-array/

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