What is time and space complexity of this code

#1

of first non repeating character

#2

@kishoretaru, if n is the number of characters in the stream
then the time complexity is o(n) as notice that for every character we insert it only once in the queue and pop it once, so for n characters we push and pop n times i.e 2n operation thus o(n) complexity and the space complexity is o(characters in the alphabet) approx o(1), as the freq array takes 26 size and the queue size also never exceed 26

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#3

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