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题目：

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

解释：

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

c++代码：

class Solution {
   public:    bool validMountainArray(vector
   
    & A) {
           int i=0,j=A.size()-1,len_A=A.size();        while(i+1
    
     A[i])            i++;        while(j-1>=0 && A[j-1]>A[j])            j--;        return i==j && i>0 && j
    
   

总结：

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