Virtual Carol Vorderman (Toying around with breadth-first search problems in scala)
'Four from the top and two small ones.'
def exprs = new Solver(List(25,50,75,100,3,6)).SolveFor(280) //> exprs: => List[main.Expression]
exprs.map( x => x.toString() + " = " + x.value ).mkString("\n") //> res0: String = ((((100 - 6) * 75) - 50) / 25) = 280
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