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### by Sumit Chourasia | Jun 07, 2020 | Category :coding | Tags : algorithmडेटा-संरचनाarrayआसानc-sharpleetcode

#### Check If N and Its Double Exist - Array - Easy - LeetCode - मिनी टीवी

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;

{
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
{
}
}

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);
}
}
}
``````

Contributed By: Sumit Chourasia
Contributed By: Sumit Chourasia
Contributed By: Sumit Chourasia
Contributed By: Sumit Chourasia