1-two-sum.cs

public class Solution {
    public int[] TwoSum(int[] nums, int target) {
    Dictionary<int, int> map = new Dictionary<int, int>();
    for (int i = 0; i < nums.Length; i++) {
        int complement = target - nums[i];
        if (map.ContainsKey(complement)) {
            return new int[] { map[complement], i };
        }
        map[nums[i]] = i;
    }
    throw new Exception("No two sum solution");
}

}