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));

As a general debugging technique, insert console.log calls into key parts of the code to display the calculated values. This will show where things have gone awry. — Matt
– Matt, Commented Feb 21, 2014 at 0:48
@Matt Thanks and I have tried that I couldn't figure out where the fault lies in the code. — M. Raza
– M. Raza, Commented Feb 21, 2014 at 0:53
A good start would be looking at newList after the slice. — RobG
– RobG, Commented Feb 21, 2014 at 1:27

ASKASK · Accepted Answer · 2014-02-21 01:05:03Z

2

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);
    }

answered Feb 21, 2014 at 1:05

ASKASK

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