Union of Arrays with Duplicates

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Time: O(n+m)

Space: O(n+m)

Problem Overview

Find union of two arrays (all unique elements from both).

Intuition

Find union of two arrays (all unique elements from both). HashSet approach.

Algorithm

1Add all elements from both arrays to a set. Size of set is the union count.

Common Pitfalls

• O(m+n). Return count of distinct elements across both arrays. Output sorted union.

Union of Arrays with Duplicates.java

Java

// Approach: HashSet of all elements from both arrays, return its size.
// Time: O(n+m) Space: O(n+m)
import java.util.*;

class Solution {
    public static int findUnion(int a[], int b[]) {
        Set<Integer> set = new HashSet<>();
        for (int ele : a)
            set.add(ele);
        for (int ele : b)
            set.add(ele);

        return set.size();
    }
}

class Solution1 {
    public static ArrayList<Integer> findUnion(int[] a, int[] b) {
        Set<Integer> set = new HashSet<>();
        for (int ele : a)
            set.add(ele);
        for (int ele : b)
            set.add(ele);

        return new ArrayList<Integer>(set);
    }
}

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