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Copy pathInsertDeleteGetRandomO1.java
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78 lines (63 loc) · 2.36 KB
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// 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.
// See: https://leetcode.com/problems/insert-delete-getrandom-o1/
package leetcode.design;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Random;
public class InsertDeleteGetRandomO1 {
// TODO: There is may be a faster alternative - try to find it.
class RandomizedSet {
List<Integer> nums = new ArrayList<>();
Map<Integer, Integer> valToIdx = new HashMap<>();
Random rand = new Random();
/** Initialize your data structure here. */
public RandomizedSet() {
}
/**
* Inserts a value to the set. Returns true if the set did not already contain
* the specified element.
*/
public boolean insert(int val) {
if (!valToIdx.containsKey(val)) {
valToIdx.put(val, nums.size());
nums.add(val);
return true;
}
return false;
}
/**
* Removes a value from the set. Returns true if the set contained the specified
* element.
*/
public boolean remove(int val) {
if (valToIdx.containsKey(val)) {
int idx = valToIdx.get(val);
int lastVal = nums.get(nums.size() - 1);
nums.set(idx, lastVal);
valToIdx.put(lastVal, idx);
nums.remove(nums.size() - 1);
valToIdx.remove(val);
return true;
}
return false;
}
/** Get a random element from the set. */
public int getRandom() {
return nums.get(rand.nextInt(nums.size()));
}
}
public static void main(String[] args) {
RandomizedSet rs = new InsertDeleteGetRandomO1().new RandomizedSet();
rs.insert(0);
rs.insert(1);
rs.remove(0);
rs.insert(2);
rs.remove(1);
System.out.println(rs.getRandom());
}
}