Optimized Solution using unordered map

[vijay4004]

Hey there!, Thanks for submitting a PR to this repo :smiley:
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• [x] My Pull Request adheres to the Contribution guidelines.
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• [x] The solution I have given is my own and not plagiarized in any form.
• [x] My solution passes all the testcases within the given constraints.
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[mergify[bot]]

Awesome :thumbsup:, Thanks for contributing :smiley:!