Merge pull request #180 from rasik210/sparsearrays

 Sparse arrays problem: C# solution

DataStructures/Arrays/Sparse Arrays/Solution.cs

@@ -0,0 +1,50 @@
+/*
+         Problem: https://www.hackerrank.com/challenges/sparse-arrays/problem
+         C# Language Version: 6.0
+         .NET Framework Version: 4.7
+         Tool Version : Visual Studio Community 2017
+         Thoughts (Key points in algorithm) :
+          - Going via sparse matrix route the complexity comes out to be O(n * q * 20) so I solved it with help of hash map which gives better complexity
+          - Scan each input string and stores its count in a hash map.
+          - For each query string, check its count in the hash map and print it on console.
+
+         Gotchas:
+            <None>
+
+         Time Complexity:  O(n + q) //n is number of input strings and q is number of queries.
+         Space Complexity: O(n + q) //a hash map (for storing frequency) and an array (for storing output counts) is addtional space requirement.
+         
+*/
+
+using System;
+using System.Collections.Generic;
+
+class Solution
+{
+    static void Main(string[] args)
+    {
+        var inputCount = int.Parse(Console.ReadLine());
+        var stringMap = new Dictionary<string, int>();
+
+        for (var i = 0; i < inputCount; i++)
+        {
+            var input = Console.ReadLine();
+            if (stringMap.ContainsKey(input))
+                stringMap[input]++;
+            else
+                stringMap.Add(input, 1);
+        }
+
+        var queryCount = int.Parse(Console.ReadLine());
+        var output = new int[queryCount];
+        for (var i = 0; i < queryCount; i++)
+        {
+            var queryString = Console.ReadLine();
+            if (stringMap.ContainsKey(queryString))
+                output[i] = stringMap[queryString];
+        }
+
+        foreach (var item in output)
+            Console.WriteLine(item);
+    }
+}

README.md

@@ -586,6 +586,7 @@
 -----|---------------- |:---------------:| --------------- | --------------- |:-------------:|:--------------:| -----
 |  |[Arrays - DS](https://www.hackerrank.com/challenges/arrays-ds/problem)| <ul><li>[C++](./DataStructures/Arrays/Arrays%20-%20DS/Solution.cpp)</li><ul> | _O(n)_ | _O(n)_| Easy | 10 | ||
 |  |[2D Array - DS](https://www.hackerrank.com/challenges/2d-array/problem)| <ul><li>[C++](./DataStructures/Arrays/2D%20Array%20-%20DS/Solution.cpp)</li><ul> | _O(1)_ | _O(1)_| Easy | 15 | ||
+|  |[Sparse Arrays](https://www.hackerrank.com/challenges/sparse-arrays/problem)| <ul><li>[C#](./DataStructures/Arrays/Sparse%20Arrays/Solution.cs)</li><ul> | _O(n + q)_ | _O(n + q)_| Medium | 25 | n = number of input strings, q = number of queries ||
 |  |[Dynamic Array](https://www.hackerrank.com/challenges/dynamic-array/problem)| <ul><li>[C#](./DataStructures/Arrays/Dynamic%20Array/Solution.cs)</li><ul> | _O(q)_ | _O(n)_| Easy | 15 | q = Number of queries ||
 
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