TangibleMonthlyAstrophysics created by byteshiva - https://repl.it/@byteshiva/TangibleMonthlyAstrophysics

index.js

/*const {createLogger , format, transports } = require('winston');
const {combine, timestamp, label, prettyPrint} = format;

const logger = createLogger({
    format: combine(
        label({label: 'algo intro'}),
        timestamp(),
        prettyPrint()
    ),
    transports : [new transports.Console()]
}); */

// @ TODO - add debug statements
// Find the missing number in Arithmetic Progression
function findMissingUsingBinarySearch(arr, low, high, diff) {
	var INT_MAX = '-- Note: should have atleast two elements';

	// There should be two elements to find the missing
	if (high <= low) return INT_MAX;

	console.log('High , low', high, low);

	var mid = low + Math.floor((high - low) / 2);

	console.log('middle number ', mid);

	if (arr[mid + 1] - arr[mid] != diff) {
		/* logger.log({
            level: 'info',
            message: 'left side of array'
        });*/
		return arr[mid] + diff;
	}

	if (mid > 0 && arr[mid] - arr[mid - 1] != diff) {
		/*logger.log({
            level: 'info',
            message: 'right side of array'
        });*/
		return arr[mid] + diff;
	}

	if (arr[mid] == arr[0] + mid * diff) {
		/*logger.log({
            level: 'info',
            message: 'Missing element using right side of array'
        });*/
		return findMissingUsingBinarySearch(arr, mid + 1, high, diff);
	}

	return findMissingUsingBinarySearch(arr, low, mid - 1, diff);
}

function findMissing(arr, n) {
	var diff = (arr[n - 1] - arr[0]) / n;

	/*logger.log({
        level: 'info',
        message: 'Difff output'
    })
    */
	return findMissingUsingBinarySearch(arr, 0, n, diff);
}

function execute() {
	var arr = [2, 4, 6, 8, 10, 12, 14];
	// var arr = [2, 4, 6, 10];

	var n = arr.length;
	/*logger.log(
        'info',
        'First  %d and last %d element', arr[n-1], arr[0]
    );
    logger.log(
        'info',
        'Diff %d element for the given arithemetic series ', (arr[n-1], arr[0])/2
    );
*/
	console.log('Missing element is ', findMissing(arr, n));
}

execute();