Problem with regex (check string for certain repetitions)

I would like to check whether in a text there are a) three consonants in a row or b) four identical letters in a row. Can someone please help me with the regular expressions?

library(tidyverse)

df <- data.frame(text = c("Completely valid", "abcdefg", "blablabla", "flahaaaa", "asdf", "another text", "a last one", "sj", "ngbas"))

consonants <- c("q", "w", "r", "t", "z", "p", "s", "d", "f", "g", "h", "k", "l", "m", "n", "b", "x")

df %>% mutate(
         invalid = FALSE, 
         # Length too short
         invalid = ifelse(nchar(text)<3, TRUE, invalid),
         # Contains three consonants in a row: e.g. "ngbas"
         invalid = ifelse(str_detect(text,"???"),  TRUE, FALSE),   # <--- Regex missing
         # More than 3 identical characters in a row: e.g. "flahaaaa" 
         invalid = ifelse(str_detect(text,"???"),  TRUE, FALSE)    # <--- Regex missing
       )

>Solution :

Three consonants in a row:

[qwrtzpsdfghklmnbx]{3}

Sequences of length > 3 of a specific char:

([a-z])(\\1){3}
    # The double backslash occurs due to its role as the escape character in strings.

The latter uses a backreference. The number represents the ordinal number assigned to the capture group (= expression in parentheses) that is referenced – in this case the character class of latin lowercase letters.

For clarity, character case is not taken into account here.

Without backreferences, the solution gets a bit lengthy:

(aaaa|bbbb|cccc|dddd|eeee|ffff|gggg|hhhh|iiii|jjjj|kkkk|llll|mmmm|nnnn|oooo|pppp|qqqq|rrrr|ssss|tttt|uuuu|vvvv|wwww|xxxx|yyyy|zzzz)

The relevant docs can be found here.