Given an integer array arr, return true if and only if it is a valid mountain array.

An array arr is a mountain array if and only if:

• arr.length $\geq 3$

• There exists some index i with $0 <$ i $<$ arr.length $- 1$ such that:

  • arr[0] $<$ arr[1] $< \dots <$ arr[i - 1] $<$ arr[i]

  • arr[i] $>$ arr[i + 1] $> \dots >$ arr[arr.length - 1]

Constraints:

• $1 \leq$ arr.length $\leq 10^4$

• $0 \leq$ arr[i] $\leq 10^4$

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