Leetcode problem solving (0941): valid mountain array (Python)

subject ：​ ​ Original link ​​（ Simple ）

solution

Time complexity

Spatial complexity

Execution time

Ans 1 (Python)

256ms (67.37%)

Ans 2 (Python)

252ms (76.14%)

Ans 3 (Python)

LeetCode Of Python Execution time , As long as there is no significant difference in time complexity , The execution time is generally of the same order of magnitude , For reference only .

Solution 1 （ One way traversal ）：

def validMountainArray(self, A: List[int]) -> bool:

 up = 0

 down = 0

 for i in range(len(A) - 1):

 if A[i] < A[i + 1]:

 if down:

 return False

 up += 1

 elif A[i] > A[i + 1]:

 down += 1

 else:

 return False

 return up > 0 and down > 0


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Solution 2 （ Bidirectional traversal ）：

def validMountainArray(self, A: List[int]) -> bool:

 idx1 = 0

 idx2 = len(A) - 1

 while idx1 < idx2:

 if A[idx1] < A[idx1 + 1]:

 idx1 += 1

 elif A[idx2 - 1] > A[idx2]:

 idx2 -= 1

 else:

 return False

 return idx1 != 0 and idx2 != len(A) - 1


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