Last Updated on 2022-11-29 by Clay
題目
Implement the RandomizedSet
class:
RandomizedSet()
Initializes theRandomizedSet
object.bool insert(int val)
Inserts an itemval
into the set if not present. Returnstrue
if the item was not present,false
otherwise.bool remove(int val)
Removes an itemval
from the set if present. Returnstrue
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 toinsert
,remove
, andgetRandom
. - There will be at least one element in the data structure when
getRandom
is called.
這個題目我們需要實作 insert()
、remove()
、getRandom()
三個 methods,而且平均時間複雜度都要求要 O(1)。
解題思路
Python 由於語法上較為彈性,所以挺好寫的;C++ 就得分別宣告一個雜湊表跟一組整數陣列來時實作。
C++ 範例程式碼
class RandomizedSet {
private:
vector<int> nums;
unordered_map<int, int> setMap;
public:
RandomizedSet() {
}
bool insert(int val) {
// Is existed
if (setMap.find(val) != setMap.end()) {
return false;
}
// Store the position of `nums`
setMap[val] = nums.size();
nums.emplace_back(val);
return true;
}
bool remove(int val) {
// Is not existed
if (setMap.find(val) == setMap.end()) {
return false;
}
// Swap the last number and the remove number
int lastNum = nums.back();
setMap[lastNum] = setMap[val];
swap(nums[nums.size()-1], nums[setMap[val]]);
// Remove the target number of `nums` and `setMap`
nums.pop_back();
setMap.erase(val);
return true;
}
int getRandom() {
return nums[rand()%nums.size()];
}
};
/**
* Your RandomizedSet object will be instantiated and called as such:
* RandomizedSet* obj = new RandomizedSet();
* bool param_1 = obj->insert(val);
* bool param_2 = obj->remove(val);
* int param_3 = obj->getRandom();
*/
Python 範例程式碼
class RandomizedSet:
def __init__(self):
self.set_map = {}
def insert(self, val: int) -> bool:
is_exist = self.set_map.get(val, False)
self.set_map[val] = True
return not is_exist
def remove(self, val: int) -> bool:
is_exist = self.set_map.get(val, False)
self.set_map.pop(val, None)
return is_exist
def getRandom(self) -> int:
return random.choice(list(self.set_map.keys()))
# 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()