# Cantor set

```ruby
func cantor (height) {
    var width = 3**(height - 1)
    var lines = height.of { "\N{FULL BLOCK}" * width }

    func trim_middle_third (len, start, index) {
        var seg = (len // 3) || return()

        for i, j in ((index ..^ height) ~X (0 ..^ seg)) {
            lines[i].replace!(Regex("^.{#{start + seg + j}}\\K."), ' ')
        }

        [0, 2*seg].each { |k|
            trim_middle_third(seg, start + k, index + 1)
        }
    }

    trim_middle_third(width, 0, 1)
    return lines
}

cantor(5).each { .say }
```

## Output:

```
█████████████████████████████████████████████████████████████████████████████████
███████████████████████████                           ███████████████████████████
█████████         █████████                           █████████         █████████
███   ███         ███   ███                           ███   ███         ███   ███
█ █   █ █         █ █   █ █                           █ █   █ █         █ █   █ █
```


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