# 941. Valid Mountain Array

**<font color=red>难度: Easy</font>**

## 刷题内容

> 原题连接

* https://leetcode.com/problems/valid-mountain-array/

> 内容描述

```
Given an array A of integers, return true if and only if it is a valid mountain array.

Recall that A is a mountain array if and only if:

A.length >= 3
There exists some i with 0 < i < A.length - 1 such that:
A[0] < A[1] < ... A[i-1] < A[i]
A[i] > A[i+1] > ... > A[B.length - 1]
 

Example 1:

Input: [2,1]
Output: false
Example 2:

Input: [3,5,5]
Output: false
Example 3:

Input: [0,3,2,1]
Output: true
 

Note:

0 <= A.length <= 10000
0 <= A[i] <= 10000 
```

## 解题方案

> 思路 1
******- 时间复杂度: O(N)******- 空间复杂度: O(1)******

sb题没什么好说的

```python
class Solution:
    def validMountainArray(self, A):
        """
        :type A: List[int]
        :rtype: bool
        """
        if len(A) < 3:
            return False
        idx = 0
        while idx < len(A) - 1 and A[idx] < A[idx+1]:
            idx += 1
        if idx == len(A) - 1 or idx == 0:
            return False
        while idx < len(A) - 1 and A[idx] > A[idx+1]:
            idx += 1
        if idx != len(A) - 1:
            return False
        return True
```
