Algorithm on Elliot Sachs

Find duplicate integer in time O(n logn) and space O(n)

Sat, 02 Jun 2018 21:46:22 +0000

Here’s how you can find a duplicate integer in a list of integers (read array) in space O(n) and time O(nlogn). This will only return the first duplicate integer in the array.

Note: This only applies for a list of integers 1..n. This won’t work otherwise.

function findDuplicate(arr) {
 var floor = 1;
 var ceiling = arr.length - 1;

 while (floor < ceiling) {
 var midpoint = Math.floor(floor + (ceiling - floor) / 2);
 var lowerRangeFloor = floor;
 var lowerRangeCeiling = midpoint;
 var upperRangeFloor = midpoint + 1;
 var upperRangeCeiling = ceiling;

 var distinctPossibleIntegersInLowerRange =
 lowerRangeCeiling - lowerRangeFloor + 1;
 var itemsInLowerRange = 0;
 arr.forEach(function (item) {
 if (item >= lowerRangeFloor && item <= lowerRangeCeiling) {
 itemsInLowerRange += 1;
 }
 });
 if (itemsInLowerRange > distinctPossibleIntegersInLowerRange) {
 floor = lowerRangeFloor;
 ceiling = lowerRangeCeiling;
 } else {
 floor = upperRangeFloor;
 ceiling = upperRangeCeiling;
 }
 }
 return floor;
}

// Example use case
let arr = [1, 2, 3, 4, 5, 4, 6, 3, 4, 6];
console.log(findDuplicate(arr)); // 3

How To Create A Singly Linked List In JavaScript

Sat, 25 Nov 2017 16:50:24 +0000

Linked Lists are relatively common and simple data structures that allow us to ’link’/chain data together. Linked Lists are useful for insertion/deletion (time complexity of O(1)), but are unfortunately not incredibly efficient when it comes to access and search (time complexity of O(n)).

The core idea behind a linked list is that you have nodes that contain two pieces of information:

The data itself
A pointer towards the next piece of data

The pointer is what chains the pieces of data together and creates the linked list.

List of Falsy Values in JavaScript & ToBoolean Algorithm

Sat, 18 Nov 2017 14:51:43 +0000

Here’s a no frills post about the falsy values in JS. In case you didn’t know, JavaScript considers some values as truthy and other as falsy. Most are deemed truthy so it’s a lot easier to simply remember the falsy ones.

You can see the truthy vs falsy evaluation in action when using an if statement. The statement takes in an expression and coerces it to a boolean value using the ToBoolean algorithm. The result is predictable and outlined in the table provided by the ECMAScript spec. Here it is below: Argument TypeResultCompletion RecordIf argument is an abrupt completion, return argument. Otherwise return ToBoolean(argument.[[value]]).UndefinedReturn false.NullReturn false.BooleanReturn argument.NumberReturn false if argument is +0, −0, or NaN; otherwise return true.StringReturn false if argument is the empty String (its length is zero); otherwise return true.SymbolReturn true.ObjectReturn true. So just to recap, the falsy values are: