1.two-sum.cs

/*
 * @lc app=leetcode id=1 lang=csharp
 *
 * [1] Two Sum
 *
 * https://leetcode.com/problems/two-sum/description/
 *
 * algorithms
 * Easy (46.77%)
 * Likes:    20481
 * Dislikes: 721
 * Total Accepted:    4.1M
 * Total Submissions: 8.8M
 * Testcase Example:  '[2,7,11,15]\n9'
 *
 * Given an array of integers nums and an integer target, return indices of the
 * two numbers such that they add up to target.
 * 
 * You may assume that each input would have exactly one solution, and you may
 * not use the same element twice.
 * 
 * You can return the answer in any order.
 * 
 * 
 * Example 1:
 * 
 * 
 * Input: nums = [2,7,11,15], target = 9
 * Output: [0,1]
 * Output: Because nums[0] + nums[1] == 9, we return [0, 1].
 * 
 * 
 * Example 2:
 * 
 * 
 * Input: nums = [3,2,4], target = 6
 * Output: [1,2]
 * 
 * 
 * Example 3:
 * 
 * 
 * Input: nums = [3,3], target = 6
 * Output: [0,1]
 * 
 * 
 * 
 * Constraints:
 * 
 * 
 * 2 <= nums.length <= 10^3
 * -10^9 <= nums[i] <= 10^9
 * -10^9 <= target <= 10^9
 * Only one valid answer exists.
 * 
 * 
 */

using System.Collections.Generic;

public class Solution
{
    public int[] TwoSum(int[] nums, int target)
    {
        Dictionary<int, int> dic = new Dictionary<int, int>();
        int[] result = new int[2];

        for (int i = 0; i < nums.Count(); i++)
        {
            if (dic.ContainsKey(target - nums[i]))
            {
                result[1] = i;
                result[0] = dic[target - nums[i]];
                return result;
            }
            else if (!dic.ContainsKey(nums[i]))
            {
                dic.Add(nums[i], i);
            }
        }
        return result;

    }
}