Two Sum

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Globalization;
 4 using System.Linq;
 5 using System.Text;
 6 using System.Threading.Tasks;
 7 
 8 namespace LeetCode
 9 {
10     class TwoSum
11     {
12         /// <summary>
13         /// via Hash
14         /// O(n)
15         /// </summary>
16         /// <param name="nums"></param>
17         /// <param name="targe"></param>
18         /// <returns></returns>
19         public int[] SolutionA(int[] nums, int target)
20         {
21             Dictionary<int,int> dic = new Dictionary<int, int>();
22             for (int i = 0; i < nums.Length; i++)
23             {
24                 if (dic.ContainsKey(target - nums[i]))
25                 {
26                     return new int[2] {dic[target-nums[i]]+1,i+1};
27                 }
28                 else if(!dic.ContainsKey(nums[i]))
29                 {
30                     dic.Add(nums[i],i);
31                 }
32             }
33             return null;
34         }
35 
36         /// <summary>
37         /// O(nlogn) + O(n) + O(n) = O(nlogn)
38         /// </summary>
39         /// <param name="nums"></param>
40         /// <param name="target"></param>
41         /// <returns></returns>
42         public int[] SolutionB(int[] nums, int target)
43         {
44             int left = 0;
45             int right = nums.Length-1;
46             int[] tempArr = new int[nums.Length];
47             nums.CopyTo(tempArr,0);
48             Array.Sort(tempArr);
49             while (left < right)
50             {
51                 if (tempArr[left] + tempArr[right] < target)
52                 {
53                     left++;
54                     continue;
55                 }else if (tempArr[left] + tempArr[right] > target)
56                 {
57                     right--;
58                     continue;
59 
60                 }
61                 else
62                 {
63                     break;
64                 }
65             }
66             int numA = tempArr[left];
67             int numB = tempArr[right];
68             int index1 = -1;
69             int index2 = -1;
70             int temp=0;
71             for (int i = 0; i < nums.Length; i++)
72             {
73                 if (nums[i] == numA || nums[i] == numB)
74                 {
75                     if (index1 == -1)
76                     { 
77                         index1 = i + 1;
78                         temp = nums[i];
79                     }
80                     else if (nums[i]==(target-temp))
81                     { 
82                         index2 = i + 1;
83                         break;
84                     }
85                 }
86             }
87             return new int[2] {index1,index2};
88         }
89     }
90 }