Problem

Given an array of integers, return the indices of the two numbers such that they add up to a specific target.
Example:
Given nums = [2, 7, 11, 15], target = 9,
Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

Solution

using System;
using System.Collections.Generic;

namespace InterviewPreperationGuide.Core.CrackingTheCodingInterview.c1q1 {
    public class Solution {
        public void Init () {
            Console.WriteLine ();
        }

        // Time: O (n)
        // Space: O (n)
        public int[] TwoSum (int[] nums, int target) {
            int[] result = new int[2];

            if (nums != null && nums.Length > 0) {
                Dictionary<int, int> map = new Dictionary<int, int> ();

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

            return result;
        }
    }
}