Insert Delete Get Random

Insert Delete Get Random hash table

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 2 is the only number in the set, getRandom always return 2.
randomSet.getRandom();
``````

Insert Delete Get Random Solution

``````class RandomizedSet {
HashMap<Integer, Integer> map;
ArrayList<Integer> values;

/** Initialize your data structure here. */
public RandomizedSet() {
map = new HashMap<Integer, Integer>();
values = new ArrayList<Integer>();
}

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

/** Removes a value from the set. Returns true if the set contained the specified element. */
public boolean remove(int val) {
if(map.containsKey(val)) {
map.remove(val);
values.remove(values.indexOf(val));
return true;
}
return false;
}

/** Get a random element from the set. */
public int getRandom() {
int random = (int)(Math.random() * values.size());
int valueToReturn = values.get(random);
return map.get(valueToReturn);
}
}``````