Comparator

The Comparator object is used in many data structures and algorithms that involve comparison and sorting of elements.

It can be created from a comparator function that has to attend to this requirements:

• The function receives two parameters (a and b) that should be compared.
• If the elements are equal, the function should return 0
• If the first parameter (a) is lower than the second(b) return a number < 0
• If the first parameter (a) is greater than the second return a number > 0

If no comparator function is passed to the Comparator object, it will use a default implementation that reproduces the behavior of the native comparison operators: >, < and ==.

function defaultComparator(a, b) {
  if (a == b) return 0;
  return a < b ? -1 : 1;
}

The Comparator Object

The Comparator Object just provides syntactic sugar for the comparator function.

Code: https://github.com/felipernb/algorithms.js/blob/master/util/comparator.js

/**
 * Initialize the comparator object with a compare function
 *
 * If the function is not passed, it will use the default
 * compare signs (<, > and ==)
 *
 * @param Function
 */
function Comparator(compareFn) {
  if (compareFn) {
    this.compare = compareFn;
  }
}

/**
 * Default implementation for the compare function
 */
Comparator.prototype.compare = function (a, b) {
  if (a == b) return 0;
  return a < b ? -1 : 1;
};

Comparator.prototype.lessThan = function (a, b) {
  return this.compare(a, b) < 0;
};

Comparator.prototype.lessThanOrEqual = function (a, b) {
  return this.lessThan(a, b) || a == b;
};

Comparator.prototype.greaterThan = function (a, b) {
  return this.compare(a, b) > 0;
};

Comparator.prototype.greaterThanOrEqual = function (a, b) {
  return this.greaterThan(a, b) || a == b;
};