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941. Valid Mountain Array

Python​

Single Loop Solution​

335 ms, 15.4MB

class Solution:
    def validMountainArray(self, arr: List[int]) -> bool:
        length = len(arr)
        if length < 3:
            return False

        top_index = 0
        is_reach_top = False
        
        for i in range(1, length):
            # Increasing
            if arr[i] > arr[i-1] and not is_reach_top:
                top_index = i
                continue

            # Decreasing
            if arr[i] < arr[i-1]:
                is_reach_top = True
                continue

            return False
        
        return top_index != 0 and top_index != length - 1

Break Loop Solution​

192 ms, 15.6MB

class Solution:
    def validMountainArray(self, arr: List[int]) -> bool:
        length = len(arr)
        if length < 3:
            return False

        i = 0
        while i < length-1:
            if arr[i] < arr[i+1]:
                i += 1
            else:
                break

        if i == 0 or i == length-1:
            return False

        while i < length-1:
            if arr[i] > arr[i+1]:
                i += 1
            else:
                break

        return i == length-1