题解 | #表达式合法判断#

# -*- coding:utf-8 -*-

class ChkExpression:
    def chkLegal(self, A):
        # write code here
        BL = set('([{')
        BR = set('}])')
        stk = []
        for a in A:
            if a in BR:
                if a == ')': b = '('
                if a == ']': b = '['
                if a == '}': b = '{'
                if stk[-1]!=b: return False
                stk.pop()
            if a in BL: stk.append(a)
        return not len(stk)