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First non-repeating character

Write a function findCharacter(str), which takes a string str as the argument. The function should return the first non-repeating character.

Instructions

• If no such character is found, return null.
• The input string str will not contain whitespace.

Example test cases

findCharacter("hello"); // Output: "h"
findCharacter("abbcddee"); // Output: "a"
findCharacter("aabbcc"); // Output: null

Hints

• You should start by building a frequency counter object.