Valid Mountain Array · Interview Problem

Leetcode

valid-mountain-array

Medium

Arrays

Two Pointers

Valid Mountain Array

Check if an array forms a valid mountain.

Acceptance 50%

Problem Statement

Core description from the backend problem record.

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

In other words, the array must strictly increase to a peak and then strictly decrease.

An integer array arr.

Return true if arr is a valid mountain array, otherwise false.

3 <= arr.length <= 10^4 0 <= arr[i] <= 10^4

Examples

Sample cases returned by the problem API.

Example 1

Input

[2,1]

Output

false

Explanation

The array length is less than 3, so it cannot form a mountain.

Example 2

Input

[3,5,5]

Output

false

Explanation

The peak is not strictly greater than the previous element.

Example 3

Input

[0,3,2,1]

Output

true

Explanation

The array has a strictly increasing sequence followed by a strictly decreasing sequence.

Loading Preptin