题目
Given an array of integers arr, return true if and only if it is a valid mountain array.
Recall that arr is a mountain array if and only if:
- arr.length >= 3
- There exists some i with 0 < i < arr.length - 1 such that:
- arr[0] < arr[1] < … < arr[i - 1] < A[i]
- arr[i] > arr[i + 1] > … > arr[arr.length - 1]
解题思路
使用两个指针从两次分别上山，判断两个指针能否相遇，且相遇的位置不是在两端
代码
class Solution:
def validMountainArray(self, arr: List[int]) -> bool:
if len(arr) < 3:
return False
i, j = 0, len(arr) - 1
while i < len(arr) - 1 and arr[i] < arr[i + 1]:
i += 1
while j >= 0 and arr[j] < arr[j - 1]:
j -= 1
return i == j and i != 0 and j != len(arr) - 1
