Java 8 # ContainsDuplicate

  Given an integer array nums, return true if any value appears at least twice in the array, and return false if every element is distinct.

import java.util.*;
import java.util.stream.*;

public class ContainsDuplicate {
    public static boolean containsDuplicate(int[] nums) {
        Set<Integer> seen = new HashSet<>();
        return Arrays.stream(nums)
                .anyMatch(n -> !seen.add(n));
    }

    public static void main(String[] args) {
        int[] nums = {1, 2, 3, 4, 1};
        System.out.println(containsDuplicate(nums)); // Output: true
    }
}