LeetCode-TwoSum.cs

// https://leetcode.com/problems/two-sum/submissions/
public class Solution {
    public int[] TwoSum(int[] nums, int target) {
        var dict = new Dictionary<int, (int num, int index)> ();

        for(int i = 0; i < nums.Length; ++i) {
            var current = nums[i];
            var required = target - current;
            
            if(dict.TryGetValue(required, out var avail)) {
                return new[] { avail.index, i };
            }
            
            dict[current] = (current, i);
        }
        
        return new int[0];
    }
}