Javascript: Given a sequence of distinct integers, split it into the maximum possible number of slices such that sorting the separate slices sorts the full sequence.

Task description

We are given an array A consisting of N distinct integers. We would like to sort array A into ascending order using a simple algorithm. First, we divide it into one or more slices $($a slice is a contiguous subarray$).$ Then we sort each slice. After that, we join the sorted slices in the same order. Write a function solution that returns the maximum number of slices for which the algorithm will return a correctly sorted array.

Examples:

$1.$ Given A $=[2,4,1,6,5,9,7],$ the function should return $3.$ The array can be split into three slices: $[2,4,1],[6,5]$ and $[9,7].$ Then, after sorting each slice and joining them together, the whole array will be sorted into ascending order.

$2.$ Given A $=[4,3,2,6,1],$ the function should return $1.$ The array cannot be split into smaller slices; it has to be sorted all at once.

$3.$ Given A $=[2,1,6,4,3,7],$ the function should return $3.$

Write an efficient algorithm for the following assumptions:

$$ N is an integer within the range $[1.\mathrm{.}100,000]$;

$$ each element of array A is an integer within the range $[1.\mathrm{.}1,000,000,000]$;

$$ the elements of A are all distinct.