2351. First Letter to Appear Twice

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Given a string s consisting of lowercase English letters, return the first letter to appear twice. Note: - A letter a appears twice before another letter b if the second occurrence of a is before the second occurrence of b. - s will contain at least one letter that appears twice. Example 1: Input: s = "abccbaacz" Output: "c" Explanation: The letter 'a' appears on the indexes 0, 5 and 6. The

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solution.cppC++17

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