941. Valid Mountain Array

1. Question:

941. Valid Mountain Array

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

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 

2. Solution:

class Solution:
    def validMountainArray(self, A):
        """
        :type A: List[int]
        :rtype: bool
        """

        size = len(A)

        if size < 3:
            return False

        max_value = max(A)
        max_index = A.index(max_value)
        
        if max_index == 0 or max_index == size-1:
            return False
        
        for i in range(1, max_index + 1):
            if A[i - 1] >= A[i]:
                return False
        

        for i in range(max_index, size - 1):
            if A[i] <= A[i + 1]:
                return False

        return True

3. Complexity Analysis

Time Complexity : O(N)

Space Complexity: O(1)