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描述
There is a programming language with only four operations and one variable X:
- ++X and X++ increments the value of the variable X by 1.
- --X and X-- decrements the value of the variable X by 1.
Initially, the value of X is 0.
Given an array of strings operations containing a list of operations, return the final value of X after performing all the operations.
Example 1:
Input: operations = ["--X","X++","X++"]
Output: 1
Explanation: The operations are performed as follows:
Initially, X = 0.
--X: X is decremented by 1, X = 0 - 1 = -1.
X++: X is incremented by 1, X = -1 + 1 = 0.
X++: X is incremented by 1, X = 0 + 1 = 1.
Example 2:
Input: operations = ["++X","++X","X++"]
Output: 3
Explanation: The operations are performed as follows:
Initially, X = 0.
++X: X is incremented by 1, X = 0 + 1 = 1.
++X: X is incremented by 1, X = 1 + 1 = 2.
X++: X is incremented by 1, X = 2 + 1 = 3.
Example 3:
Input: operations = ["X++","++X","--X","X--"]
Output: 0
Explanation: The operations are performed as follows:
Initially, X = 0.
X++: X is incremented by 1, X = 0 + 1 = 1.
++X: X is incremented by 1, X = 1 + 1 = 2.
--X: X is decremented by 1, X = 2 - 1 = 1.
X--: X is decremented by 1, X = 1 - 1 = 0.
Note:
1 <= operations.length <= 100
operations[i] will be either "++X", "X++", "--X", or "X--".
解析
根据题意，就是给出来某种编程语言的的四种操作和一个变量 X ：
- 如果操作为 ++X 或者 X++ 表示对 X 做加一操作
- 如果操作为 --X 或者 X-- 表示对 X 做减一操作
我们初始化变量 X 为 0 ，问在执行了一系列的 operations 之后得到的最终值是多少。
其实思路很简单，就是遍历 operations 中的每一个操作 op ，如果字符串 op 中包含 - 表示的是减一操作，如果字符串 op 中包含 + 表示的是加一操作，遍历结束得到的结果就是答案。
解答
class Solution(object):
def finalValueAfterOperations(self, operations):
"""
:type operations: List[str]
:rtype: int
"""
result = 0
for op in operations:
if '-' in op:
result -= 1
elif '+' in op:
result += 1
return result
运行结果
Runtime: 24 ms, faster than 99.62% of Python online submissions for Final Value of Variable After Performing Operations.
Memory Usage: 13.6 MB, less than 13.41% of Python online submissions for Final Value of Variable After Performing Operations.
解析
另外我们可以用 python 的内置函数 sum ，代码简洁易懂。
sum(iterable[, start]) 函数对序列进行求和计算，传入的对象可以是列表、元组、集合等可迭代对象。例如：
>>>sum([0,1,2])
3
解答
class Solution(object):
def finalValueAfterOperations(self, operations):
"""
:type operations: List[str]
:rtype: int
"""
return sum(1 if '+' in o else -1 for o in operations)
运行结果
Runtime: 28 ms, faster than 99.23% of Python online submissions for Final Value of Variable After Performing Operations.
Memory Usage: 13.3 MB, less than 86.21% of Python online submissions for Final Value of Variable After Performing Operations.
原题链接：leetcode.com/problems/fi…
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