349.Intersection of Two Arrays

Method 1

Given two integer arrays nums1 and nums2, return an array of their intersection. Each element in the result must be unique and you may return the result in any order.

Example 1

Input: nums1 = [ 1,2,2,1 ], nums2 = [ 2,2 ]
Output: [2]

Example 2

Input: nums1 = [ 4,9,5 ], nums2 = [ 9,4,9,8,4 ]
Output: [9,4]
Explanation: [4,9] is also accepted.

Method 1

【O(n + m) time | O(min(n, m)) space】

package Leetcode.Array;

import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;

/**
 * @author zhengstars
 * @date 2024/10/16
 */
public class IntersectionOfTwoArrays {
    public static int[] intersection(int[] nums1, int[] nums2) {
        // Create a HashSet to store unique elements from nums1
        Set<Integer> set1 = new HashSet<>();
        // Create a HashSet to store the intersection elements
        Set<Integer> resultSet = new HashSet<>();

        // Add all elements from nums1 to set1 (automatically removes duplicates)
        for (int num: nums1) {
            set1.add(num);
        }

        // Check each element in nums2
        // If it exists in set1, it's an intersection element
        for (int num: nums2) {
            if(set1.contains(num)){
                resultSet.add(num);
            }
        }

        // Convert HashSet to array for return value
        int[] result = new int[resultSet.size()];
        int i = 0;
        for (int num: resultSet) {
            result[i++] = num;
        }

        return result;
    }

    /**
     * Main method containing test cases
     * @param args command line arguments (not used)
     */
    public static void main(String[] args) {
        // Test Case 1: Basic test with duplicates
        // Expected output: [2]
        int[] nums1 = {1, 2, 2, 1};
        int[] nums2 = {2, 2};
        int[] result1 = intersection(nums1, nums2);
        System.out.println("Test Case 1:");
        System.out.println("Output: " + Arrays.toString(result1));

        // Test Case 2: No intersection
        // Expected output: []
        int[] nums3 = {1, 2, 3};
        int[] nums4 = {4, 5, 6};
        int[] result2 = intersection(nums3, nums4);
        System.out.println("Test Case 2:");
        System.out.println("Output: " + Arrays.toString(result2));

        // Test Case 3: Multiple intersections
        // Expected output: [4,9]
        int[] nums5 = {4, 9, 5};
        int[] nums6 = {9, 4, 9, 8, 4};
        int[] result3 = intersection(nums5, nums6);
        System.out.println("Test Case 3:");
        System.out.println("Output: " + Arrays.toString(result3));

        // Test Case 4: Empty array
        // Expected output: []
        int[] nums7 = {};
        int[] nums8 = {1, 2, 3};
        int[] result4 = intersection(nums7, nums8);
        System.out.println("Test Case 4:");
        System.out.println("Output: " + Arrays.toString(result4));

        // Test Case 5: Identical arrays
        // Expected output: [1,2,3]
        int[] nums9 = {1, 2, 3};
        int[] nums10 = {1, 2, 3};
        int[] result5 = intersection(nums9, nums10);
        System.out.println("Test Case 5:");
        System.out.println("Output: " + Arrays.toString(result5));
    }
}

Method 1

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