## 2017年2月22日 星期三

### 【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.
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 ")".

Correctness：100%、Performance：100%
```python 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 ```