fix(pairwise): Clarification of instructions, closes #9037

[gristow]

Pre-Submission Checklist

• Your pull request targets the staging branch of FreeCodeCamp.
• Branch starts with either fix/, feature/, or translate/ (e.g. fix/signin-issue)
• You have only one commit (if not, squash them into one commit).
• All new and existing tests pass the command npm test. Use git commit --amend to amend any fixes.

Type of Change

• Small bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds new functionality)
• Breaking change (fix or feature that would change existing functionality)
• Add new translation (feature adding new translations)

Checklist:

• Tested changes locally.
• Closes currently open issue (replace XXXX with an issue no): Closes Pairwise challenge description is vague #9037

Description

Clarification of instructions to better match the test cases. Replace this paragraph, in the original wording:

If multiple pairs are possible that have the same numeric elements but different indices, return the smallest sum of indices. Once an element has been used, it cannot be reused to pair with another.

Which seemed to suggest that in the test case pairwise([0, 0, 0, 0, 1, 1], 1)===10 only the pair of indices {0, 4} should be used, to fit the criterion 'if multiple pairs are possible ... return the smallest sum of indices.' However, the expected behavior of the test is that indices {0, 4} and {1, 5} should both be used.

To reflect that, the paragraph is replaced with:

You may use multiple pairs that have the same numeric elements but different indices. Each pair should use the lowest possible available indices. Once an element has been used it cannot be reused to pair with another element.

[camperbot]

@gristow thanks for the PR.
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[camperbot]

@gristow updated the pull request.