1
func firstUniqChar(_ s: String) -> Character {
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    let strArr = Array(s)
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    var dp: [Character : Int] = [:]
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    var indexs: [Character] = []
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6
    strArr.forEach {
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        if dp[$0] != nil {
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            if let idx = indexs.firstIndex(of: $0) {
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                indexs.remove(at: idx)
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            }
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        }
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        else {
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            dp[$0] = 1
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            indexs.append($0)
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        }
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    }
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    return indexs.first ?? " "
19
}