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Python | Find all distinct pairs with difference equal to k
• Last Updated : 25 Nov, 2019

Given a list of integers and a positive integer k, write a Python program to count all distinct pairs with difference equal to k.

Examples:

```Input : [1, 5, 3, 4, 2], k = 3
Output : [(5, 2), (4, 1)]

Input : [8, 12, 16, 4, 0, 20], k = 4
Output : [(8, 4), (12, 8), (16, 12), (4, 0), (20, 16)]
```

Approach #1 : Python list comprehension

We will use list comprehension using two loops using ‘e1’ and ‘e2’ that will traverse given list. We check if e1-e2 == k or not and return the (e1, e2) tuple respectively. Finally, a list with required tuples will be returned.

 `# Python3 program to Find all distinct  ` `# pairs with difference equal to k ` ` `  `def` `findPairs(lst, k): ` `     `  `    ``return` `[(e1, e2) ``for` `e1 ``in` `lst  ` `            ``for` `e2 ``in` `lst ``if` `(e1``-``e2 ``=``=` `k)] ` `         `  `# Driver code ` `lst ``=` `[``1``, ``5``, ``3``, ``4``, ``2``] ` `k ``=` `3` `print``(findPairs(lst, k)) `

Output:

```[(5, 2), (4, 1)]
```

Approach #2 :

This is an efficient approach with respect to the above approach as it uses only O(n) space. We take an empty list to store the output. Then, we use a loop with iterator ‘e’ to traverse through given list. In every iteration, we check is e+k i.e the required pair integer for e is available or not. If yes, we append the tuple to ‘res’.

 `# Python3 program to Find all distinct  ` `# pairs with difference equal to k ` ` `  `def` `findPairs(lst, k): ` `    ``res ``=` `[] ` `    ``for` `e ``in` `lst: ` `        ``if` `e ``+` `k ``in` `lst: ` `            ``res.append(``tuple``((e, e ``+` `k))) ` `             `  `    ``return` `res ` `     `  `# Driver code ` `lst ``=` `[``1``, ``5``, ``3``, ``4``, ``2``] ` `k ``=` `3` `print``(findPairs(lst, k)) `

Output:

```[(1, 4), (2, 5)]
```

Approach #3 : `combinations()` from `itertools` module

The best approach is to use the inbuilt function from itertools module. combinations() produces an iterator over tuples of all combinations of n elements in inputs. We make the use of these combinations and output those having ‘k’ difference.

 `# Python3 program to Find all distinct  ` `# pairs with difference equal to k ` `from` `itertools ``import` `combinations ` ` `  `def` `findPairs(lst, k): ` `    ``return` `[(x, y) ``for` `x, y ``in` `combinations(lst, r ``=` `2``) ` `                   ``if` `abs``(x ``-` `y) ``=``=` `k] ` `             `  `# Driver code ` `lst ``=` `[``1``, ``5``, ``3``, ``4``, ``2``] ` `k ``=` `3` `print``(findPairs(lst, k)) `

Output:

```[(1, 4), (5, 2)]
```

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