{ "data": { "question": { "questionId": "2427", "questionFrontendId": "2351", "boundTopicId": null, "title": "First Letter to Appear Twice", "titleSlug": "first-letter-to-appear-twice", "content": "

Given a string s consisting of lowercase English letters, return the first letter to appear twice.

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Note:

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Example 1:

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\nInput: s = "abccbaacz"\nOutput: "c"\nExplanation:\nThe letter 'a' appears on the indexes 0, 5 and 6.\nThe letter 'b' appears on the indexes 1 and 4.\nThe letter 'c' appears on the indexes 2, 3 and 7.\nThe letter 'z' appears on the index 8.\nThe letter 'c' is the first letter to appear twice, because out of all the letters the index of its second occurrence is the smallest.\n
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Example 2:

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\nInput: s = "abcdd"\nOutput: "d"\nExplanation:\nThe only letter that appears twice is 'd' so we return 'd'.\n
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Constraints:

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Most standard library headers are already included automatically for your convenience.

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OpenJDK 17 . Java 8 features such as lambda expressions and stream API can be used.

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Python 2.7.12.

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C# 10 with .NET 6 runtime

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Ruby 3.1

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Swift 5.5.2.

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Go 1.17.6.

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Python 3.10.

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With bcmath module

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TypeScript 4.5.4, Node.js 16.13.2.

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Dart 2.17.3

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