'''
栈
实现语言: Python
有次序的数据集, 每个数据仅从栈顶一端加入和从数据集中移除
'''

class Stack:
    def __init__(self):
        self.items = []

    def isEmpty(self):
        return self.items == []

    # 入栈
    def push(self, item):
        self.items.append(item)

    # 出栈
    def pop(self):
        return self.items.pop()

    # Peek 偷看；一瞥，看一眼；（计算机）读取数据
    def peek(self):
        return self.items[len(self.items) - 1]

    def size(self):
        return len(self.items)


'''
使用栈进行简单括号匹配
'''
def matches(open, close):
    opens = "([{"
    closers = ")]}"
    return opens.index(open) == closers.index(close)


def parChecker(symbolString):
    s = Stack()
    balanced = True
    index = 0
    while index < len(symbolString) and balanced:
        symbol = symbolString[index]
        if symbol in "([{":
            s.push(symbol)
        else:
            if s.isEmpty():
                balanced = False
            else:
                top = s.pop()
                if not matches(top, symbol):
                    balanced = False

        index += 1

    if balanced and s.isEmpty():
        return True
    else:
        return False