#!/usr/bin/env python
# -*- coding: utf-8 -*-

from collections import OrderedDict


def find_index_of_first_unique_char(string):
    seen_once = OrderedDict()                       # LinkedHashMap
    seen_many = set()                               # HashSet
    for index, char in enumerate(string):           # O(N)
        if char in seen_many:                       # O(1)
            continue
        elif char in seen_once:                     # O(1)
            seen_many.add(char)                     # O(1)
            seen_once.pop(char)                     # O(1)
        else:
            seen_once[char] = index                 # O(1)
    if not seen_once:                               # O(1)
        return -1
    else:
        # get the first item
        return seen_once.popitem(last=False)[1]     # O(1)


assert find_index_of_first_unique_char("") == -1
assert find_index_of_first_unique_char("aa") == -1
assert find_index_of_first_unique_char("baa") == 0
assert find_index_of_first_unique_char("zabcddd") == 0
assert find_index_of_first_unique_char("this is my string") == 1
assert find_index_of_first_unique_char("this this is my string") == 13
assert find_index_of_first_unique_char("this this is my string add an m") == 14