'''
Given a string s consisting of small English letters, find and return the first instance of a non-repeating character in it. 

If there is no such character, return '_'.
'''

def solution(s):
    order = []
    count = {}
    for c in s:
        if c in count:
            count[c] +=1
        else:
            count[c] = 1
            order.append(c)
    for c in order:
        if count[c] == 1:
            return c
    return '_'
    return -1;

print(solution("abacabaabacaba")
     ) #output "_"

print(solution("abacabad")
     ) #output "c"

print(solution("bcccccccccccccyb")) #output "y"