First Non-Repeating Character in a Stream
Intermediate
Characters arrive one at a time. After each character, write down the first character that has appeared only once so far, or # if there is none. Return the string of those answers (one per arriving character).
For "aabc" the answers are a, #, b, b, so the result is "a#bb".
Examples
Example 1
Input:
first_non_repeating_stream('aabc')
Output:
'a#bb'
Example 2
Input:
first_non_repeating_stream('zz')
Output:
'z#'
Constraints
0 <= len(s) <= 200000scontains lower-case letters.
Theory
Go to TheoryKeywords
dsa-sheetstack-and-queuequeues-and-deques
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