find all pairs in an array with sum equal to given number

Author: ahsankamal

beginners/pair_with_given_sum.cpp

@@ -0,0 +1,80 @@
+#include<iostream>
+
+using namespace std;
+
+int main()
+{
+cout<<"Enter the size of array\n";
+long n;
+cin>>n;
+cout<<"Enter "<<n<<" space seperated integers\n";
+long *arr = new long[n];
+for(long i=0;i<n;i++){
+	cin>>arr[i];
+}
+
+sort(arr, arr+n);//in ascending order
+	cout<<"Sorted array:\n";
+	for(long i=0;i<n;i++)
+	{
+		cout<<arr[i]<<" ";
+	}
+	cout<<endl;
+
+long sum;
+cout<<"Enter the value of sum\n";
+cin>>sum;
+
+long left=0,right=n-1;
+bool pair_exist = false;
+
+while(left<right){
+	long left_plus_right = arr[left] + arr[right];
+	if(left_plus_right==sum)
+		{
+			cout<<"Pair:("<<arr[left]<<","<<arr[right]<<")\n";
+			left++;//to find next pair whose sum is equal to given sum
+			pair_exist = true;
+		}	
+	else if(left_plus_right<sum)//move left pointer
+		left++;
+	else//move right pointer
+		right--;
+}
+
+if(pair_exist == false){
+	cout<<"No pair exist with sum equal to "<<sum<<endl;
+} 
+
+	return 0;
+}
+
+
+/* 
+Test case1:
+Enter the size of array
+8
+Enter 8 space seperated integers
+12 3 5 6 2 7 8 4 
+Sorted array:
+2 3 4 5 6 7 8 12 
+Enter the value of sum
+8
+Pair:(2,6)
+Pair:(3,5)
+
+
+Test case 2:
+Enter the size of array
+10
+Enter 10 space seperated integers
+1 2 3 5 6 4 7 8 10 5
+Sorted array:
+1 2 3 4 5 5 6 7 8 10 
+Enter the value of sum
+9
+Pair:(1,8)
+Pair:(2,7)
+Pair:(3,6)
+Pair:(4,5)
+*/