一个只包含’(‘, ‘)’, ‘[‘, ‘]’, ‘{‘, ‘}’的字符串，判断其是否合法。
合法的条件是左右括号必须正好完全匹配。
比如:
‘()[]{}’和’()’合法
‘(]’和’{)’不合法。
python实现:
def isValidParentheses(l):
stack = []
for c in l:
if c in (‘(‘, ‘[‘, ‘{‘):
stack.append(c)
elif c in (‘)’, ‘]’, ‘}’):
if len(stack) == 0:
return False top = stack.pop()
if c == ‘)’ and top != ‘(‘:
return False
if c == ‘]’ and top != ‘[‘:
return False
if c == ‘}’ and top != ‘{‘:
return False
else:
return False
return len(stack) == 0
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