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380. Insert Delete GetRandom O(1).java
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380. Insert Delete GetRandom O(1).java
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class RandomizedSet {
List<Integer> indexList;
HashMap<Integer, Integer> map;
/** Initialize your data structure here. */
public RandomizedSet() {
map = new HashMap<>();
indexList = new ArrayList<>();
}
/**
* 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))
return false;
indexList.add(val);
int index = indexList.size() - 1;
map.put(val, index);
return true;
}
/**
* Removes a value from the set. Returns true if the set contained the specified
* element.
*/
public boolean remove(int val) {
if (!map.containsKey(val))
return false;
int index = map.get(val);
map.remove(val);
if (index < indexList.size() - 1) {
int size = indexList.size();
int temp = indexList.get(size - 1);
map.put(temp, index);
indexList.set(index, temp);
}
indexList.remove(indexList.size() - 1);
return true;
}
/** Get a random element from the set. */
public int getRandom() {
int index = (int) (Math.random() * indexList.size());
return indexList.get(index);
}
}
/**
* 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();
*/