Count pairs with given sum Python

PROGRAM TO FIND THE NUMBER OF PAIRS OF INTEGERS IN THE ARRAY WHOSE SUM IS EQUAL TO SUM

# Function to return the count of pairs

# from arr with the given sum

def pairs_count(arr, n, sum):

      

    # To store the count of pairs

    ans = 0

  

    # Sort the given array

    arr = sorted(arr)

  

    # Take two pointers

    i, j = 0, n - 1

  

    while (i < j):

          

        # If sum is greater

        if (arr[i] + arr[j] < sum):

            i += 1

  

        # If sum is lesser

        elif (arr[i] + arr[j] > sum):

            j -= 1

              

        # If sum is equal

        else:

              

            # Find the frequency of arr[i]

            x = arr[i]

            xx = i

            while (i < j and arr[i] == x):

                i += 1

  

            # Find the frequency of arr[j]

            y = arr[j]

            yy = j

            while (j >= i and arr[j] == y):

                j -= 1

  

            # If arr[i] and arr[j] are same

            # then remove the extra number counted

            if (x == y):

                temp = i - xx + yy - j - 1

                ans += (temp * (temp + 1)) // 2

            else:

                ans += (i - xx) * (yy - j)

  

    # Return the required answer

    return ans

  

# Driver code

arr = [1, 5, 7, 5, -1]

n = len(arr)

sum = 6

  

print(pairs_count(arr, n, sum))







OUTPUT

3

CREDITS: https://www.geeksforgeeks.org/count-pairs-with-given-sum-set-2/