# 941. Valid Mountain Array 有效的山脉数组

@TOC

## # 题目描述

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:

1. `0 <= A.length <= 10000`
2. `0 <= A[i] <= 10000 `

## # 解题方法

``````class Solution:
def validMountainArray(self, A):
"""
:type A: List[int]
:rtype: bool
"""
N = len(A)
if N < 3:
return False
i = 0
while i < N - 1:
if A[i] < A[i + 1]:
i += 1
else:
break
if i == 0 or i == N - 1: return False
while i < N - 1:
if A[i] > A[i + 1]:
i += 1
else:
break
return i == N - 1
``````

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

## # 日期

2018 年 11 月 18 日 —— 出去玩了一天，腿都要废了 2018 年 11 月 24 日 —— 周六快乐