我要写一个只做加法和减法的表达式求值器.我有一个简单的算法来做到这一点;但是,我有一些实现问题.
"(" <expression1> <operator> <expression2> ")"
这是我的算法
String evaluate( String expression ) if expression is digit return expression else if expression is "(" <expression1> <operator> <expression2> ")" cut the brackets out of it expression1 = evaluate( <expression1> ) operator = <operator> expression2 = evaluate( <expression2> ) if operator is + expression1 + expression2 else if operator is - expression1 - expression2
我的问题是解析< expression1>< operator>和< expression2>从表达.我怎样才能做到这一点?
谢谢,
-Ali