380. Insert Delete GetRandom O(1)

  • 38.8%

https://leetcode.com/problems/insert-delete-getrandom-o1/

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.
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> 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();
>

java

169ms, September 12, 2016

https://discuss.leetcode.com/topic/53216/java-solution-using-a-hashmap-and-an-arraylist-along-with-a-follow-up-131-ms

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public class RandomizedSet {
ArrayList<Integer> nums;
HashMap<Integer, Integer> locs;
java.util.Random rand = new java.util.Random();
/** Initialize your data structure here. */
public RandomizedSet() {
nums = new ArrayList<Integer>();
locs = new HashMap<Integer, Integer>();
}

/** Inserts a value to the set. Returns true if the set did not already contain the specified element. */
public boolean insert(int val) {
boolean contain = locs.containsKey(val);
if(contain) return false;
locs.put(val, nums.size());
nums.add(val);
return true;
}

/** Removes a value from the set. Returns true if the set contained the specified element. */
public boolean remove(int val) {
boolean contain = locs.containsKey(val);
if(!contain) return false;
int loc = locs.get(val);
if(loc < nums.size() - 1){
int lastone = nums.get(nums.size()-1);
nums.set(loc, lastone);
locs.put(lastone, loc);
}
locs.remove(val);
nums.remove(nums.size()-1);
return true;
}

/** Get a random element from the set. */
public int getRandom() {
return nums.get(rand.nextInt(nums.size()));
}
}

/**
* Your RandomizedSet object will be instantiated and called as such:
* RandomizedSet obj = new RandomizedSet();
* boolean param_1 = obj.insert(val);
* boolean param_2 = obj.remove(val);
* int param_3 = obj.getRandom();
*/

cpp

112ms, September 12, 2016

https://discuss.leetcode.com/topic/53286/ac-c-solution-unordered_map-vector

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class RandomizedSet {
public:
/** Initialize your data structure here. */
RandomizedSet() {

}

/** Inserts a value to the set. Returns true if the set did not already contain the specified element. */
bool insert(int val) {
if(m.find(val) != m.end()) return false;
nums.emplace_back(val);
m[val] = nums.size() - 1;
return true;
}

/** Removes a value from the set. Returns true if the set contained the specified element. */
bool remove(int val) {
if(m.find(val)==m.end()) return false;
int last = nums.back();
m[last] = m[val];
nums[m[val]] = last;
nums.pop_back();
m.erase(val);
return true;
}

/** Get a random element from the set. */
int getRandom() {
return nums[rand() % nums.size()];
}
private:
vector<int> nums;
unordered_map<int, int> m;
};

/**
* 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

145ms, September 12, 2016

https://discuss.leetcode.com/topic/53344/simple-solution-in-python

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class RandomizedSet(object):

def __init__(self):
"""
Initialize your data structure here.
"""
self.nums, self.pos = [], {}

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], self.pos[last] = 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
"""
return self.nums[random.randint(0, len(self.nums)-1)]



# 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()
谢谢你,可爱的朋友。