Merge pull request #47 from Dvd1234/main

Code to compute the pairs having a given sum

Array/CountPairsWithGivenSum.java

@@ -0,0 +1,39 @@
+package java;
+
+import java.util.*;
+/*
+Given an array of N integers, and a number sum, the task is to find the number of pairs of integers
+in the array whose sum is equal to sum.
+ */
+
+class PairWithGivenSum {
+
+    static int getPairsCount(int arr[], int n, int k)
+    {
+        HashMap<Integer, Integer> m = new HashMap<>();
+        int count = 0;
+        for (int i = 0; i < n; i++) {
+            if (m.containsKey(k - arr[i])) {
+                count += m.get(k - arr[i]);
+            }
+            if (m.containsKey(arr[i])) {
+                m.put(arr[i], m.get(arr[i]) + 1);
+            }
+            else {
+                m.put(arr[i], 1);
+            }
+        }
+        return count;
+    }
+
+    public static void main(String[] args)
+    {
+        int arr[] = { 1, 5, 7, -1, 5 };
+        int sum = 6;
+        System.out.print("Count of pairs is " + getPairsCount(arr, arr.length, sum));
+    }
+}
+/*
+Time Complexity: O(n),
+Auxiliary Space: O(n),
+ */