Count pairs with given sum #10282
Count pairs with given sum #10282
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…arr/Python_hacktoberfest into count_pairs_with_given_sum
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I am lost. What is the value of solving this? In what situation would this algorithm be useful? The first half of the algorithm could be a one-liner by using a defaultdict or a Counter. |
| >>> pairs_with_sum([1,7,6,2,5,4,3,1,9,8],7) | ||
| 4 | ||
| """ | ||
| d: dict = {} |
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| d: dict = {} | |
| d = {} |
This type is inferred. Also try to use more descriptive variable names
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So I had to add that because it wasn't passing all the three tasks. I know we don't have to mention the type but I did so just to pass all the three tasks
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It gave some type not specified error
| d[i] -= 1 | ||
| if req_sum - i in d and d[req_sum - i] != 0: | ||
| ans += d[req_sum - i] | ||
| d[i] += 1 |
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You are subtracting one, and then adding one after an irrelevant if statement. Why?
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So the reason I included that is because let's say the given number is 8 and you have 4 in your array. Now if u don't decrement d[4] by 1 then from the code it will check if 4 exists in the dictionary and as it does ans will be incremented. So even though there is only one 4 in the array it will still be considered. I could remove that and put if d[req-i]!=1
This is the solution to an array leetcode problem. Yes you can use defaultdict for the first half. I just thought this will be more descriptive and easier to comprehend. I can change that. I think this problem is good for beginners to understand why hashing is required for these types of array questions |
Please add a URL to the problem in the docstring at the top of the file as recommended in CONTRIBUTING.md. Please use a defaultdict or Counter as this repo is for visitors who want to study quality algorithms. If reviewers are confused by it then the code or its documentation must be improved before it can be merged. |
So when I'm using defaultdict it says it needs type annotation for d. This was the same error I was getting before also thats the reason i didnt use defaultdict before. How do I fix this |
I have added the problem link in the docstring |
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| Count the no of pairs in a given array with given sum | ||
| Problem URL- https://practice.geeksforgeeks.org/problems/count-pairs-with-given-sum5022/0 |
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| Count the no of pairs in a given array with given sum | |
| Problem URL- https://practice.geeksforgeeks.org/problems/count-pairs-with-given-sum5022/0 | |
| Given an array of integers and an integer req_sum, find the number of pairs of array | |
| elements whose sum is equal to req_sum. | |
| https://practice.geeksforgeeks.org/problems/count-pairs-with-given-sum5022/0 |
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* added power_of_4 * deleted power_of_4 * added pairs_with_given_sum * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci * updated the comment * updated return hint * updated type hints * updated the variable * updated annotation * updated code * updated code * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci * added the problem link and used defaultdict * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci * corrected import formatting * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci * Update pairs_with_given_sum.py * Update data_structures/arrays/pairs_with_given_sum.py --------- Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com> Co-authored-by: Christian Clauss <cclauss@me.com>
Describe your change:
I have added the solution to the problem for counting the no of pairs in an array with the given sum in the most optimal way
Checklist: