bigOlogn.js

// Binary Search(Iterative Approach)

var binarySearch = function (array, number) {
    var start = 0;
    var end = array.length - 1;

    // Iterate while start not meets end 
    while (start <= end) {

        // Find the mid index 
        var mid = Math.floor((start + end) / 2);

        // If element is present at mid, return True 
        if (array[mid] === number) return true;

        // Else look in left or right half accordingly 
        else if (array[mid] < number)
            start = mid + 1;
        else
            end = mid - 1;
    }

    return false;
};

function findNumber(array, number) {
    if (binarySearch(array, number, 0, array.length-1)) {
        return('Number 5 exist in the array');
    } else {
        return('Number 5 not found!');
        
    }
}

var numberArray = [1, 3, 4, 2, 5, 7, 6, 8, 9];
var searched_number = 5;

// will display Number 5 exist in the array
console.log(findNumber(numberArray, searched_number));

// **********************************************************************************
// - In this case the run time of this script is: O(logn)
// - this is a script that implement binary search through iterative approach. 
// - we use a while loop, which runs until it hits the base condition 
// - i.e start becomes greater than end.
// - best case scenario is when the element we are looking for is stored in the 
// - middle of the array.(which means the script will only run one time)
// - Worst case scenario is when the element we are looking for is stored either 
// - at the end or begining of the array
// **********************************************************************************