Find the Intersection of Two Arrays

📌 Definition:

📖 Detailed Explanation:

Put one array’s elements in a hash set, then scan the other and collect elements present in the set (moving matches into a result set to avoid repeats). O(n + m). Sorting both and using two pointers is the O(1)-extra-space alternative.

💻 Solutions:

• Java
• JavaScript
• Python

public static Set<Integer> intersection(int[] a, int[] b) {
    Set<Integer> set = new HashSet<>();
    for (int x : a) set.add(x);
    Set<Integer> out = new LinkedHashSet<>();
    for (int x : b) if (set.contains(x)) out.add(x);
    return out;
}

function intersection(a, b) {
  const set = new Set(a);
  return [...new Set(b.filter(x => set.has(x)))];
}

def intersection(a, b):
    return list(set(a) & set(b))

🔑 Key Points:

• Hash set of one array, probe with the other
• Collect matches in a set to dedupe
• O(n + m) time
• Two-pointer on sorted inputs is the low-space option

🌍 Real-World Example: