I’m trying to perform my first binary search in javascript. But I’m failing to see what’s holding me back from getting the result I would expect from my code.

This is my code:

function search(arr, target, start = 0, end = arr.length - 1) {
  if (start > end) {
    console.log('Not found!');
    return -1;
  }

  const middle = Math.floor((start + end) / 2);

  if (arr[middle] === target) {
    console.log(`${target} found at index ${middle}`);
    return middle;
  }

  if (arr[middle] > target) {
    return search(target, start, middle - 1);
  }

  if (arr[middle] < target) {
    return search(target, middle + 1, end);
  }

}

const arr = ['a', 'b', 'c', 'x', 'y', 'z'];
console.log(search(arr, 'b'));

So when I run the above code my result is the following…

I’m getting
Not found!

What i’m expecting
b found at index 1
1

I’m fairly new to algorithms, but I’m failing to see what’s going on here. Even when just copying the code from the guide I’m following, I also get a different result then the teacher is getting. So there must be something underlying wrong I would assume?

Thanks in advance for taking time to help me out! I’m trying to learn and get a better understanding here. So please do elaborate if I’m totally misunderstanding the obvious here.

I’m running the program with node on my windows 10 machine and im using nodejs v18.14.1

>Solution :

The issue with your code is that you are not passing the entire array to the recursive calls of the search function.

In the cases where you are recursively calling the search function, you are only passing the target, start, and end parameters, but not the arr array itself. Therefore, the search function is not searching through the entire array, and this is causing it to return 'Not found!' even when the target is present in the array.

Try the following fix:

function search(arr, target, start = 0, end = arr.length - 1) {
  if (start > end) {
    console.log('Not found!');
    return -1;
  }

  const middle = Math.floor((start + end) / 2);

  if (arr[middle] === target) {
    console.log(`${target} found at index ${middle}`);
    return middle;
  }

  if (arr[middle] > target) {
    return search(arr, target, start, middle - 1);
  }

  if (arr[middle] < target) {
    return search(arr, target, middle + 1, end);
  }

}

const arr = ['a', 'b', 'c', 'x', 'y', 'z'];
console.log(search(arr, 'b'));