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Maximum length of mountain in an array using JavaScript
Mountain Subsequence
We call any (contiguous) subarray sub (of arr) a mountain if the following properties hold −
sub.length >= 3
There exists some 0 < i < sub.length - 1 such that sub[0] < sub[1] < ... sub[i-1] < sub[i] > B[i+1] > ... > sub[sub.length - 1]
Problem
We are required to write a JavaScript function that takes in an array of numbers, arr, as the first and the only argument.
Our function is supposed to return the length of the greatest mountain subsequence present in the array arr, if there exists any, 0 otherwise.
For example, if the input to the function is
Input
const arr = [3, 2, 5, 8, 4, 3, 6];
Output
const output = 5;
Output Explanation
Because the desired subarray is −
[2, 5, 8, 4, 3]
Example
Following is the code −
const arr = [3, 2, 5, 8, 4, 3, 6];
const mountainLength = (arr = []) => {
let max = 0
for(let left = 0; left < arr.length; left++) {
let right = left
while(arr[right] < arr[right + 1]) {
right++
}
const top = right
while(right > left && arr[right] > arr[right + 1]) {
right++
}
if(right > top && top > left) {
max = Math.max(max, right - left + 1)
left = right
left--
}
}
return max
}
console.log(mountainLength(arr));Output
5
Updated on: 24-Apr-2021
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