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  1. r <- "(?(DEFINE)(?<n>[-+]?\\d+(?:\\.\\d+)?)(?<a>\\s*[-+*\\/]\\s*)(?<g>\\((?:(?&n)|(?&g))(?&a)(?:(?&n)|(?&g))\\)))^(?&g)$"
  2. x <- c("(14.0 + 46.0)", "((5.0 - 50.0) - 15.0)", "(15.0 - (5.0 - 50.0))", "(15.0 - (5.0 - 50.0)")
  3. grep(r, x, perl=TRUE)
Success #stdin #stdout 0.2s 39012KB
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https://ideone.com/MCYO54
language:
R (R 3.5.2)
created:
6 years ago
visibility:
public

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