#1106

Parsing A Boolean Expression

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Description

A boolean expression is an expression that evaluates to either true or false. It can be in one of the following shapes:

- 't' that evaluates to true.

- 'f' that evaluates to false.

- '!(subExpr)' that evaluates to the logical NOT of the inner expression subExpr.

- '&(subExpr1, subExpr2, ..., subExprn)' that evaluates to the logical AND of the inner expressions subExpr1, subExpr2, ..., subExprn where n >= 1.

- '|(subExpr1, subExpr2, ..., subExprn)' that evaluates to the logical OR of the inner expressions subExpr1, subExpr2, ..., subExprn where n >= 1.

Given a string expression that represents a boolean expression, return the evaluation of that expression.

It is guaranteed that the given expression is valid and follows the given rules.

Example 1:

Input: expression = "&(|(f))"

Output: false

Explanation:

First, evaluate |(f) --> f. The expression is now "&(f)".

Then, evaluate &(f) --> f. The expression is now "f".

Finally, return false.

Example 2:

Input: expression = "|(f,f,f,t)"

Output: true

Explanation: The evaluation of (false OR false OR false OR true) is true.

Example 3:

Input: expression = "!(&(f,t))"

Output: true

Explanation:

First, evaluate &(f,t) --> (false AND true) --> false --> f. The expression is now "!(f)".

Then, evaluate !(f) --> NOT false --> true. We return true.

Solution