JavaScript/Search/ExponentialSearch.js

/*
 * Exponential Search
 *
 * The algorithm consists of two stages. The first stage determines a 
 * range in which the search key would reside if it were in the list. 
 * In the second stage, a binary search is performed on this range.
 * 
 *
 *  
 */

function binarySearch(arr, x, floor, ceiling) {
    // Middle index
    let mid = Math.floor((floor + ceiling) / 2);

    // If value is at the mid position return this position
    if (arr[mid] === x) {
        return mid;
    }

    if(floor > ceiling) return -1;

    // If the middle element is great than the value 
    // search the left part of the array
    if (arr[mid] > value) {
        return binarySearch(arr, value, floor, mid - 1);
        //If the middle element is lower than the value
        //search the right part of the array
    } else {
        return binarySearch(arr, value, mid + 1, ceiling);
    }


}


function exponentialSearch(arr, length, value) {
    // If value is the first element of the array return this position 
    if (arr[0] == value) {
        return 0;
    }

    // Find range for binary search 
    let i = 1;
    while (i < length && arr[i] <= value) {
        i = i * 2;
    }

    // Call binary search for the range found above 
    return binarySearch(arr, value, i / 2, Math.min(i, length));
}

let arr = [2, 3, 4, 10, 40, 65 , 78 , 100];
let value = 78;
let result = exponentialSearch(arr, arr.length, value);

if (result < 0) {
    console.log("Element not found");
} else {
    console.log("Element found at position :" + result);
}