using System;
using System.Collections.Generic;

namespace MyCompiler {
    class Program {
        public static void Main(string[] args) {
            var sol = new Solution();
            
            int[] nums = new int[] {1,2,3,4,5};        
            Console.WriteLine("input: [{0}]", string.Join(", ", nums));

            for (var target = 0; target < 12; target++) {
                int[] output = sol.TwoSum(nums, target);
                Console.WriteLine($"target={target} : " + "[{0}]", string.Join(", ", output));
            }            
        }
    }
    
    class Solution {        
        public int[] TwoSum(int[] nums, int target) {
            var prevMap = new Dictionary<int, int>();
            
            for (var i = 0; i < nums.Length; i++) {
                int diff = target - nums[i];
                if (prevMap.ContainsKey(diff)) {
                    return new int[] {prevMap[diff], i};
                }
                prevMap[nums[i]] = i;
            }
            
            return new int[] {};
        }
    }
}