10/18 檢查是否先嚴格遞增後再嚴格遞減

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] < arr[i]
  • arr[i] > arr[i + 1] > ... > arr[arr.length - 1]

 

Example 1:

Input: arr = [2,1]
Output: false

Example 2:

Input: arr = [3,5,5]
Output: false

Example 3:

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

 

Constraints:

• 1 <= arr.length <= 104
• 0 <= arr[i] <= 104

 

class Solution:

    def validMountainArray(self, arr: List[int]) -> bool:

        #嚴格遞增後嚴格遞減

        top = max(arr)

        top_index = arr.index(top)

        n= len(arr)

        up,down=0,0

       

        for i in range(1,top_index+1):

            if arr[i] -arr[i-1] <= 0 :

                return False

            up = 1

           

           

        for i in range(top_index, n-1):

            down = 1

            if arr[i+1] - arr[i]  >= 0 :

                return False

        if up and down:

            return True    

        else:

            return False

       

           

---------------------------

class Solution:
    def validMountainArray(self, arr: List[int]) -> bool:
        i_last = len(arr) - 1
        left = 0
        right = i_last

        # move right
        while left < i_last and (arr[left] < arr[left + 1]):
            left += 1

        if left == i_last:
            return False

        while right > 0 and (arr[right] < arr[right - 1]):
            right -= 1
        
        if right == 0:
            return False
        
        return left == right

-------------------------

class Solution:
    def validMountainArray(self, arr: List[int]) -> bool:
        start_hill_flag = False
        up_flag = True
        prev_num=arr[0]
        
        if len(arr) <3 or arr[0] >= arr[1]:
            return False
        
        for i in range(1,len(arr)):
            current_num = arr[i]
            if current_num == prev_num:
                return False
            
    
            
            if up_flag:
                if current_num < prev_num:
                    up_flag = False
            else:
                if current_num > prev_num:
                    return False
            
            prev_num = current_num
        
        if up_flag:
            return False
        return True