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LeetCode-381-Insert-Delete-GetRandomO(1)-Duplicates-allowed.java
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LeetCode-381-Insert-Delete-GetRandomO(1)-Duplicates-allowed.java
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class RandomizedCollection {
private java.util.Random rand = new Random();
LinkedList<Integer> vals; // list of vals
HashMap<Integer, Set<Integer>> locs; // <val, set<idx>> pair
/** Initialize your data structure here. */
public RandomizedCollection() {
vals = new LinkedList<>();
locs = new HashMap<>();
}
/** Inserts a value to the collection. Returns true if the collection did not already contain the specified element. */
public boolean insert(int val) {
boolean notContains = !locs.containsKey(val);
if (notContains) locs.put(val, new HashSet<>());
// locs.computeIfAbsent(val, k -> new HashSet<>());
locs.get(val).add(vals.size());
vals.add(val);
return notContains;
}
/** Removes a value from the collection. Returns true if the collection contained the specified element. */
public boolean remove(int val) {
if (!locs.containsKey(val)) return false;
int lastIdx = vals.size() - 1;
int lastVal = vals.get(lastIdx);
if (lastVal != val) {
// replace val with lastVal
int currIdx = locs.get(val).iterator().next();
locs.get(lastVal).add(currIdx);
locs.get(val).remove(currIdx);
vals.set(currIdx, lastVal);
}
locs.get(lastVal).remove(lastIdx);
vals.remove(lastIdx);
if (locs.get(val).isEmpty()) {
locs.remove(val);
}
return true;
}
/** Get a random element from the collection. */
public int getRandom() {
return vals.get(rand.nextInt(vals.size()));
}
}
/**
* Your RandomizedCollection object will be instantiated and called as such:
* RandomizedCollection obj = new RandomizedCollection();
* boolean param_1 = obj.insert(val);
* boolean param_2 = obj.remove(val);
* int param_3 = obj.getRandom();
*/