Check if Array is a Mountain

ArrayTwo Pointers

Given an array of integers, determine if it represents a 'mountain'. A 'mountain' array is defined as one that:

You must check if the input array follows this pattern and return true if it is a mountain array and false otherwise.

Example 1

Input

[
  2,
  1,
  4,
  7,
  3,
  2
]

Output

true

Explanation. The array increases to element 7, then decreases, forming a mountain shape.

Example 2

Input

[
  5,
  5,
  5,
  5
]

Output

false

Explanation. The array doesn't increase and decrease, it remains constant, hence it's not a mountain.

Example 3

Input

[
  0,
  3,
  2,
  1
]

Output

true

Explanation. The array strictly increases to 3 and then decreases, forming a valid mountain.

Example 4

Input

[
  1,
  2,
  3,
  4,
  5
]

Output

false

Explanation. The array only increases and does not decrease, hence it is not a mountain.

Example 5

Input

[
  10,
  6,
  5,
  4,
  3,
  2,
  1
]

Output

false

Explanation. The array only decreases and never increases to a peak, hence it is not a mountain.

Follow-up: How would your solution change if you needed to find the index of the peak element in the mountain array?

Constraints:

The input array will contain at least 3 integers, and all elements will be non-negative integers.