Udemy: Master Coing Interview - Hash Tables - #78

using System;
using System.Collections.Generic;

class MainClass {
    // Given an array, return the first recurring value
    // Example input: {2, 5, 1, 2, 3, 5, 1, 2, 4} should return 2
    // Example input: {2, 1, 1, 2, 3, 4, 1, 2, 4} should return 1
    // Example input: {2, 3, 4, 5} should return undefined (-1)
    static void Main() {
        Console.WriteLine("Hello World!");
        int[] array1 = {2, 5, 1, 2, 3, 5, 1, 2, 4};
        int[] array2 = {2, 1, 1, 2, 3, 4, 1, 2, 4};
        int[] array3 = {2, 3, 4, 5};
        
        Console.WriteLine("First recurring value in array1 is "
        + FirstRecurring(array1));
        Console.WriteLine("First recurring value in array2 is "
        + FirstRecurring(array2));
        Console.WriteLine("First recurring value in array3 is "
        + FirstRecurring(array3));
    }
    
    public static int FirstRecurring(int[] array) {
        Dictionary<int, int> dict = new Dictionary<int, int>();
        for (int i = 0; i < array.Length; i++) {
            if (dict.ContainsKey(array[i])) {
                return array[i];
            }
            dict.Add(array[i], 1);
        }
        return -1;
    }
}