Added a folder of C++ problems and attached a question of hashmap with optimised solution

Program's_Contributed_By_Contributors/Cpp_code/Pair_with_difference_k.cpp

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+Question:- 
+
+Pairs with difference K
+
+You are given with an array of integers and an integer K. You have to find and print the count of all such pairs which have difference K.
+
+Note: Take absolute difference between the elements of the array.
+
+Input Format:
+The first line of input contains an integer, that denotes the value of the size of the array. Let us denote it with the symbol n.
+The following line contains n space separated integers, that denote the value of the elements of the array.
+The following line contains an integer, that denotes the value of K.
+
+Output format :
+The first and only line of output contains count of all such pairs which have an absolute difference of K. 
+
+Constraints :
+0 <= n <= 10^4
+
+Time Limit: 1 sec
+
+Sample Input 1 :
+4 
+5 1 2 4
+3
+Sample Output 1 :
+2
+
+Sample Input 2 :
+4
+4 4 4 4 
+0
+Sample Output 2 :
+6  
+
+Code:- 
+
+#include <bits/stdc++.h>
+using namespace std;
+
+
+int getPairsWithDifferenceK(int *arr, int n, int k) 
+{
+	unordered_map<int,int> m;
+    int ans=0,val=0;
+    for(int i=0;i<n;i++)
+    {
+          val=arr[i]+k;
+          ans=ans+m[val];  
+
+        if(k!=0)
+        {
+          val=arr[i]-k;
+          ans=ans+m[val];  
+        }
+        m[arr[i]]++;
+    }
+    return ans;
+}
+
+int main() 
+{
+    int n;
+    cin >> n;
+
+    int *input = new int[n];
+
+    for (int i = 0; i < n; i++) 
+    {
+        cin >> input[i];
+    }
+
+    int k;
+    cin >> k;
+
+    cout << getPairsWithDifferenceK(input, n, k);
+
+    delete[] input;
+}