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380. Insert Delete GetRandom O(1)
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();思路分析
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/**
* 自己实现
*/
class RandomizedSet {
private List<Integer> nums;
private Map<Integer, Integer> idex;
private Random random;
public RandomizedSet() {
nums = new ArrayList<>();
random = new Random();
idex = new HashMap<>();
}
public boolean insert(int val) {
if (idex.containsKey(val)) {
return false;
} else {
nums.add(val);
idex.put(val, nums.size() - 1);
return true;
}
}
public boolean remove(int val) {
if (!idex.containsKey(val)) {
return false;
} else {
int i1 = idex.get(val);
if (i1 != idex.size() - 1) {
Integer value = nums.get(nums.size() - 1);
nums.set(i1, value);
idex.put(value, i1);
}
idex.remove(val);
nums.remove(nums.size() - 1);
return true;
}
}
public int getRandom() {
return nums.get(random.nextInt(nums.size()));
}
}