Problem Statement:- Given an array of N integers, and an integer K, find the number of pairs of elements in the array whose sum is equal to K.

**def countpairs(x,length,sum):
    count = 0
    for i in range(0,length):
       for j in range(i 1,length):
            print(x[i],x[j])   
            if(x[i] x[j]==sum):
                count =1
    print(count)


x  = [1, 1, 1, 1]
sum = 2
length=len(x)
countpairs(x,length,sum)
Output:= 6**
This is My solution used in VS code.

My Question:- whenever I am running the same code in gfg it is not accepting the code giving me this error. I even have tried the same code in the online compiler there also it is running correctly.

This Is the gfg code which i have written 
class Solution:
    def getPairsCount(self, arr, K, N):
        count = 0
        for i in range(0,N):
           for j in range(i 1,N): 
                if(arr[i] arr[j]==K):
                    count =1
        return count


#Initial Template for Python 3

if __name__ == '__main__':
    tc = int(input())
    while tc > 0:
        n, k = list(map(int, input().strip().split()))
        arr = list(map(int, input().strip().split()))
        ob = Solution()
        ans = ob.getPairsCount(arr, n, k)
        print(ans)
        tc -= 1


Error
if(arr[i] arr[j]==K):
IndexError: list index out of range

CodePudding user response：

There's no added value in using a class for this. You just need:-

def getPairsCount(arr, K):
  count = 0
  for i in range(len(arr)-1):
    if arr[i]   arr[i 1] == K:
      count  = 1
  return count

EDIT:

Previous answer assumed that only adjacent elements were to be considered. If that's not the case then try this:-

import itertools

def getPairsCount(arr, K):
    count = 0
    for c in itertools.combinations(sorted(arr), 2):
        if c[0]   c[1] == K:
            count  = 1
    return count

data = [1, 2, 1, 4, -1]
print(getPairsCount(data, 3))

CodePudding user response：

We do not need two loops for this question. Here is something that runs in O(n):

def countpairs(list_,K):
    count = 0
    set_ = set(list_)
    pairs_ = []
    
    for val in list_:
        if K - val in set_:
            # we ensure that pairs are unordered by using min and max
            pairs_.append ( (min(val, K-val), max(val, K-val)) )
            count =1

    set_pairs = set(pairs_)
    
    print ("Pairs which sum up to ",K," are: ", set_pairs)

    return len(set_pairs)




x  = [1,4,5,8,2,0,24,7,6]
sum_ = 13
print ("Total count of pairs summming up to ", sum_, " = ", countpairs(x, sum_))

Output:

Pairs which sum up to  13  are:  {(6, 7), (5, 8)}
Total count of pairs summming up to  13  =  2

The idea is that if two values should sum to a value K, we can iterate through the array and check if there is another element in the array which when paired with the current element, sums up to K. The inner loop in your solution can be replaced with a search using the in. Now, we need this search to be fast (O(1) per element), so we create a set out of our input array (set_ in my example).