Implement a function listFormat(items, options) that joins an array of strings into a single formatted string.

The function should support an options object with the following properties:

• sorted: boolean — if true, sort items alphabetically.
• length: number — show only the first length items, and append "and X other(s)" for remaining items.
• unique: boolean — remove duplicates.
• Ignore empty strings and invalid length values (0, negative, etc).

Examples

listFormat([]); // ''
listFormat(['Bob']); // 'Bob'
listFormat(['Bob', 'Alice']); // 'Bob and Alice'
listFormat(['Bob', 'Ben', 'Tim', 'Jane', 'John']);
// 'Bob, Ben, Tim, Jane and John'

listFormat(['Bob', 'Ben', 'Tim', 'Jane', 'John'], { length: 3 });
// 'Bob, Ben, Tim and 2 others'

listFormat(['Bob', 'Ben', 'Tim', 'Jane', 'John'], { length: 4 });
// 'Bob, Ben, Tim, Jane and 1 other'

listFormat(['Bob', 'Ben', 'Tim', 'Jane', 'John'], { length: 3, sorted: true });
// 'Ben, Bob, Jane and 2 others'

listFormat(['Bob', 'Ben', 'Tim', 'Jane', 'John', 'Bob'], { length: 3, unique: true });
// 'Bob, Ben, Tim and 2 others'

listFormat(['Bob', 'Ben', '', '', 'John']); // 'Bob, Ben and John'