indexes.ts

let num = [0,8,-2,5,0];
let val = 0;

const startAndEndOfVal = (numArr: Array<number>, val: number) => {
   let indexes = numArr.sort().reduce((acc: Array<number>, cur: number, index: number) => {
        if(cur === val){
            acc.push(index)
        }
        return acc
    }, []);

   if(indexes.length === 0) {
     return [-1, -1];
   }

   return [indexes[0], indexes[indexes.length - 1]];
}

console.log(startAndEndOfVal(num, val));

Yes @meekg33k I agree with your concern, sort function is not the most efficient.
And according to MDN
The time and space complexity of the sort cannot be guaranteed as it depends on the implementation..

Also looking at my algo again there is a subtle error, I forgot to add the comparator for the sort function, this will only be noticeable for some kind of numbers eg [40, 100, 10, 200] which will be [ 10, 100, 200, 40 ] when sorted.

I did some research and found bubble sort, it looks fast but worst case senerio for bubble sort is n2 which is not as efficient as sort function see comparison table https://en.wikipedia.org/wiki/Sorting_algorithm.

To get an efficient algorithm (in my view) for this merge sort seems like the way to go.

Here is my update:

// merge sort
const merge = (left: Array<number>, right: Array<number>) => {
  const resArr: Array<number> = [];
  let leftArrayIndex: number = 0;
  let rightArrayIndex: number = 0;

  while (leftArrayIndex < left.length && rightArrayIndex < right.length) {
    left[leftArrayIndex] < right[rightArrayIndex]
      ? resArr.push(left[leftArrayIndex++])
      : resArr.push(right[rightArrayIndex++]);
  }
  return [
    ...resArr,
    ...left.slice(leftArrayIndex),
    ...right.slice(rightArrayIndex),
  ];
};

// notice it is recursive
const mergeSort = (arr: Array<number>) =>
  arr.length <= 1
    ? arr
    : merge(
        mergeSort(arr.slice(0, Math.floor(arr.length / 2))),
        mergeSort(arr.slice(Math.floor(arr.length / 2)))
      );

const startAndEndOfVal = (numArr: Array<number>, val: number) => {
  let indexes = mergeSort(numArr).reduce(
    (acc: Array<number>, cur: number, index: number) => {
      if (cur === val) {
        acc.push(index);
      }
      return acc;
    },
    []
  );

  if (indexes.length === 0) {
    return [-1, -1];
  }

  return [indexes[0], indexes[indexes.length - 1]];
};

// TEST
let num = [0, 8, -2, 5, 0];
let val = 0;

console.log(startAndEndOfVal(num, val));

Hello @charleslukes, this is a really interesting solution. You were able to implement the merge-sort, that is amazing!

That said, do you think there's a way we could have solved this problem without having to sort the array?

I have written a blog post here sharing my solution to this problem - a solution that avoids sorting the array. Please read through and let me know what you think.

I hope this was a good learning experience for you. Thank you once again for participating once again and see you on Friday for Week 4 of #AlgorithmFridays.