Can Regex Detect and Count Vertical 'X' Patterns in ASCII Art?-PHP Tutorial-php.cn

Can Regex Detect and Count Vertical 'X' Patterns in ASCII Art?

Mary-Kate Olsen

Release： 2024-11-16 12:15:03

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Can Regex Detect and Count Vertical

Finding Vertical X Patterns in ASCII with Regex

Problem Statement

In an ASCII image like the below:

....X.......
..X..X...X....
X.X...X..X.....
X....XXXXXX.....
X..XXX...........
.....X..........
..............X
..X...........X....
..X...........X....X...
....X.....

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We aim to detect the following pattern:

X
X
X

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where three Xs are aligned vertically.

Questions

Is it possible to determine if such formations exist using regex?
If so, is it possible to count the number of occurrences?

Answer to Question 1

Yes, the following regex can identify the presence of vertical X formations:

(?xm)                    # ignore comments and whitespace, ^ matches beginning of line
^                        # beginning of line
(?:
    .                    # any character except \n
    (?=                  # lookahead
        .*+\n            # go to next line
        ( ?+ . )       # add a character to the 1st capturing group
        .*+\n            # next line
        ( ?+ . )       # add a character to the 2nd capturing group
    )
)*?                      # repeat as few times as needed
X .*+\n                  # X on the first line and advance to next line
?+                     # if 1st capturing group is defined, use it, consuming exactly the same number of characters as on the first line
X .*+\n                  # X on the 2nd line and advance to next line
?+                     # if 2st capturing group is defined, use it, consuming exactly the same number of characters as on the first line
X                        # X on the 3rd line

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Online Demo: https://regex101.com/r/YxPeXe/1

Answer to Question 2

Indirect Solution

To count the number of formations, we can perform the following substitution:

regex =>

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where regex is the above pattern. The resulting string length will equal the count of matches.

Online Demo: https://regex101.com/r/Tx6R63/1

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