Problem Statement

Given an integer array arr, return true if arr is a valid mountain array. Otherwise, return false.

The array is called a valid mountain array if:

• arr.length > 2
• 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]

Examples

Example 1:

• Input: arr = [4, 5, 6, 7, 8, 7, 6, 5]
• Expected Output: true
• Justification: The elements increase from 4 to 8 and then decrease from 8 back to 5, forming a mountain shape.

Example 2:

• Input: arr = [1, 2, 3, 4, 5]
• Expected Output: false
• Justification: The elements only increase and there's no decrease after a peak, hence not forming a mountain.

Example 3:

• Input: arr = [9, 8, 7, 6, 5]
• Expected Output: false
• Justification: The elements decrease from the start without an initial increase, failing to form a mountain shape.

Try it yourself

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