First non-repeating character in a stream of characters

Given a string A denoting a stream of lowercase alphabets. You have to make new string B.

B is formed such that we have to find first non-repeating character each time a character is inserted to the stream and append it at the end to B. If no non-repeating character is found then append '#' at the end of B.

1 <= length of the string <= 100000

The only argument given is string A.

Return a string B after processing the stream of lowercase alphabets A.

Input 1:

 A = "abadbc"

Input 2:

 A = "abcabc"

Output 1:

 "aabbdd"

Output 2:

 "aaabc#"

Explanation 1:

    "a"      -   first non repeating character 'a'
    "ab"     -   first non repeating character 'a'
    "aba"    -   first non repeating character 'b'
    "abad"   -   first non repeating character 'b'
    "abadb"  -   first non repeating character 'd'
    "abadbc" -   first non repeating character 'd'

Explanation 2:

    "a"      -   first non repeating character 'a'
    "ab"     -   first non repeating character 'a'
    "abc"    -   first non repeating character 'a'
    "abca"   -   first non repeating character 'b'
    "abcab"  -   first non repeating character 'c'
    "abcabc" -   no non repeating character so '#'