Binary Search Code

Question

I am coding my own function for a binary search algorithm and I can't seem to find the discrepancies in logic. When ever I search for 4 it does not return the ideal response.

Code Below:

var list = [1,2,3,4,6,7,13,18,19];

function binarySearch(list,number) {
    var newList = list;
    while (newList.length >= 1) {
        var halfNum = Math.round(newList.length/2);
            if (newList[halfNum] === number) {
            return "Number Found";
        } else if (newList[halfNum] < number) {
            newList = newList.slice(halfNum + 1,newList.length - 1);
        } else {
            newList = newList.slice(0,halfNum - 1);
        }
    }
}


console.log(binarySearch(list,4));

Answer 1

The problem here is that you are doing the ranges wrong. the javascript slice function cuts the array into the interval [start,finish), and by that I mean that it does not include the end index in the new array

So you shoudl change this:

    } else if (newList[halfNum] < number) {
        newList = newList.slice(halfNum + 1,newList.length - 1);
    } else {
        newList = newList.slice(0,halfNum - 1);
    }

To this:

    } else if (newList[halfNum] < number) {
        newList = newList.slice(halfNum + 1,newList.length);
    } else {
        newList = newList.slice(0,halfNum);
    }