WeChall - Training - Regex

Challenge

4-level regex training on WeChall. Each level requires the shortest possible regex pattern, submitted with delimiters (e.g. /pattern/).

Solution

Level 1 — match empty string: /^$/

Level 2 — match the string "wechall" exactly: /^wechall$/

Level 3 — match image filenames wechall.ext or wechall4.ext with valid extensions (jpg, gif, tiff, bmp, png):

/^wechall4?\.(?:gif|tiff|png|jpg|bmp)$/

• 4? makes the 4 optional (wechall or wechall4)
• (?:...) non-capturing group for the extensions (shortest possible)

Level 4 — same as L3 but capture the filename without extension:

/^(wechall4?)\.(?:gif|tiff|png|jpg|bmp)$/

• (wechall4?) capture group returns wechall or wechall4