LeetCode: Valid Mountain Array Solution

Approach

Make sure the array:

• has one peak only
• does not have any valley
• does not have flat road (2 equal adjacent elements)

Implementation

1/**
2 * @param {number[]} arr
3 * @return {boolean}
4 */
5var validMountainArray = function (arr) {
6  let peakCount = 0
7  let valleyCount = 0
8  let hasFlatWay = false
9
10  for (let i = 1; i < arr.length - 1; i++) {
11    if (arr[i] === arr[i - 1] || arr[i] === arr[i + 1]) {
12      hasFlatWay = true
13    }
14    if (arr[i] > arr[i - 1] && arr[i] > arr[i + 1]) {
15      peakCount++
16    }
17    if (arr[i] < arr[i - 1] && arr[i] < arr[i + 1]) {
18      valleyCount++
19    }
20  }
21
22  return peakCount === 1 && valleyCount === 0 && !hasFlatWay
23}