Simple Encoder

Create a function that takes a string str and performs simple encoding as per the following method:

• Replace all single occurrence characters with [
• Replace all characters with two or more occurrences with ]

Return the final string after modification.

Examples

simple_encoder("Mubashir") ➞ "[[[[[[[["
# '[' for each character

simple_encoder("Matt") ➞ "[[]]"
# ']' for both 't'

simple_encoder("eD  aBiT") ➞ "[[]][[[["
# Two spaces in between

Notes

• Strings can contain lower and uppercase letters. Treat them equally (i.e. A = a, B = b).
• Spaces are also characters.