TwoSum

using System;
using System.Collections.Generic;

namespace TwoSum
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] array1 = { 2, 7, 11, 15 };
            int target1 = 9;
            (int first1, int second1) = new TwoTermsFinder().FindIndexes(array1, target1);
            Console.WriteLine($"Two terms have indexes {first1} and {second1}");

            int[] array2 = { 13, 7, 9, 1, 11, 18 };
            int target2 = 19;
            (int first2, int second2) = new TwoTermsFinder().FindIndexes(array2, target2);
            Console.WriteLine($"Two terms have indexes {first2} and {second2}");
        }
    }

    class TwoTermsFinder
    {
        Dictionary<int, int> number_index = new Dictionary<int, int>();
        public (int, int) FindIndexes(int[] array, int target)
        {
            for(int i = 0; i < array.Length; i++)
            {
                if (number_index.ContainsKey(target - array[i]))
                    return (number_index[target - array[i]], i);
                number_index.Add(array[i], i);
            }
            return (0, 0);
        }
    }
}