Two Sum是LeetCode基礎的演算法~

例如~ 有一個array放 7, 11, 5, 2~ 然後~target是9~

最後它的輸出會是 0,3~

學習目標: Two sum的概念及實務

學習難度: ☆☆☆

using System;

using System.Collections.Generic;

namespace ConsoleApp1
{
    class MainProgram
    {
        static int[] Twosum(int[] numbers, int target)
        {
            //用Dictionary實作

            Dictionary<int, int> dictionary = new Dictionary<int, int>();

            for (int i = 0; i < numbers.Length; i++)
            {
                int temp = target - numbers[i];

                if (dictionary.ContainsKey(temp))
                {
                    //dictionary[temp]是key(數值)，會回傳value(索引)

                    return new int[] { dictionary[temp], i };
                }

                else
                {
                    // 因為我們要求索引，所以這裡的value是i

                    dictionary[numbers[i]] = i;
                }
            }
            return null;
        }

        static void Main()
        {
            int[] arrays = new int[] { 7, 11, 5, 2 };

            int target = 9;

            Twosum(arrays, target);
        }
    }
}

參考資料:

https://ithelp.ithome.com.tw/articles/10217042