Check If N and Its Double Exist - Array - Easy - LeetCode

Given an array arr of integers, check if there exist two integers N and M such that N is the double of M ( i.e. N = 2 * M).

More formally check if there exists two indices i and j such that :

i != j

0 <= i, j < arr.length

arr[i] == 2 * arr[j]

Example 1:

Input: arr = [10,2,5,3]

Output: true

Explanation: N = 10 is the double of M = 5,that is, 10 = 2 * 5.

Example 2:

Input: arr = [7,1,14,11]

Output: true

Explanation: N = 14 is the double of M = 7,that is, 14 = 2 * 7.

Example 3:

Input: arr = [3,1,7,11]

Output: false

Explanation: In this case does not exist N and M, such that N = 2 * M.

Constraints:

2 <= arr.length <= 500

-10^3 <= arr[i] <= 10^3

Solution:

using System;
using System.Collections.Generic;
using System.Text;

namespace LeetCode.AskGif.Easy.Array
{
 public class CheckIfExistSoln
 {
 public bool CheckIfExist(int[] arr)
 {
 var map = new Dictionary<int, int>();
 for (int i = 0; i < arr.Length; i++)
 {
 if (map.ContainsKey(arr[i]))
 {
 map[arr[i]]++;
 }
 else
 {
 map.Add(arr[i], 1);
 }
 }

 if (map.ContainsKey(0) && map[0] == 2)
 {
 return true;
 }

 map.Remove(0);

 for (int i = 0; i < arr.Length; i++)
 {
 if(map.ContainsKey(arr[i] * 2))
 {
 return true;
 }
 }

 return false;
 }
 }
}

Time Complexity: O(n)

Space Complexity: O(n)

Unit Tests:

using LeetCode.AskGif.Easy.Array;
using Microsoft.VisualStudio.TestTools.UnitTesting;
using System;
using System.Collections.Generic;
using System.Text;

namespace CodingUnitTest.Easy.Array
{
 [TestClass]
 public class CheckIfExistSolnTests
 {
 [TestMethod]
 public void CheckIfExistSoln_First()
 {
 var arr = new int[] { 10, 2, 5, 3 };
 var output = true;
 var res = new CheckIfExistSoln().CheckIfExist(arr);

 Assert.AreEqual(res, output);
 }

 [TestMethod]
 public void CheckIfExistSoln_Second()
 {
 var arr = new int[] { 7, 1, 14, 11 };
 var output = true;
 var res = new CheckIfExistSoln().CheckIfExist(arr);

 Assert.AreEqual(res, output);
 }

 [TestMethod]
 public void CheckIfExistSoln_Third()
 {
 var arr = new int[] { 3, 1, 7, 11 };
 var output = false;
 var res = new CheckIfExistSoln().CheckIfExist(arr);

 Assert.AreEqual(res, output);
 }

 [TestMethod]
 public void CheckIfExistSoln_Fourth()
 {
 var arr = new int[] { -2, 0, 10, -19, 4, 6, -8 };
 var output = false;
 var res = new CheckIfExistSoln().CheckIfExist(arr);

 Assert.AreEqual(res, output);
 }
 }
}