Function that returns first non repeating character in a string.
Parameters: A string. Output : A char.
A new ,empty , dictionary is initialised. Using a for loop iterate through the string , char by char . For every char, the following is done : --> if it is not in the dictionary , add it and set the value to 1 .(The key is the char ). -->if it is already in the dictionary , increase it's value.
Now there is a dictionary with the key value pair being a char and it's number of ocurences. Iterate through that dictionary untill a key value pair having value=1 is found, and return the key (meaning , the char)