Unique Character

Problem

Given a string s, find the first non-repeating character in it and return its index. If it does not exist, return -1.

Examples

uniqChar("algorithm")
// returns 0
// The character  'a' is the first non-repeating character

uniqChar("javaj")
// returns 2
// The character  'v' is the first non-repeating character

uniqChar("abccba")
// returns -1
// All characters are appearing more than once