Here are some regular expression patterns: \\d one digit \\d? optional digit \\d zero or more digits \\d+ one or more digits The regular expression pttern to match one digit is ^\\d$ Write the regular expression pattern to match one digit. Examples: 2 5 Write the regular expression pattern to match two digits Examples: 16 65 Write the regular expression pattern to match three digits Examples: 911 209 Write the regular expression pattern for one optional digit followed by one digit Examples: 65 5 Write the regular expression pattern for one optional digit followed by one optional digit followed by one digit Examples: 100 65 4 Write the regular expression pattern for two digits followed by an optional digit followed by an optional digit Examples: 20 123 2020 Write the regular expression pattern for an optional digit followed by an optional digit followed by two digits Examples: 20 123 2020