【Python】Codility in Python : Lesson 7 - Stacks and Queues【Brackets】

Stacks and Queues 第一題：【Brackets】
Determine whether a given string of parentheses is properly nested.

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A string S consisting of N characters is considered to be properly nested
if any of the following conditions is true:

S is empty;
S has the form "(U)" or "[U]" or "{U}" where U is a properly nested string;
S has the form "VW" where V and W are properly nested strings.
For example, the string "{[()()]}" is properly nested but "([)()]" is not.

Write a function:

　　def solution(S)

that, given a string S consisting of N characters,
returns 1 if S is properly nested and 0 otherwise.

For example, given S = "{[()()]}", the function should return 1
and given S = "([)()]", the function should return 0, as explained above.

Assume that:
　　N is an integer within the range [0..200,000];
　　string S consists only of the following characters: "(", "{", "[", "]", "}" and/or ")".

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方法一：用 append 和 pop 實作 stack 的概念
Correctness：100%、Performance：100%

def solution(S):
  stack = []
  for sign in S:
    if sign == '(' or sign == '[' or sign =='{':
      stack.append(sign)
    else:
      if len(stack) == 0:
        return 0
      stackLast = stack[-1]
      if sign == ')' and stackLast == '(':
        stack.pop()
      elif sign == ']' and stackLast == '[':
        stack.pop()
      elif sign == '}' and stackLast == '{':
        stack.pop()
      else:
        return 0

  return 1 if len(stack) == 0 else 0

完整練習題 source code 請參閱：github