A Common-Sense Guide to Data Structures and Algorithms in JavaScript, Volume 1

A Linear Solution

What follows is another implementation of the hasDuplicateValue function that doesn’t rely on nested loops. It’s a bit clever, so let’s first look at how it works and then we’ll see if it’s any more efficient than our first implementation.

function hasDuplicateValue(array) {
  const existingNumbers = [];

  for (let i = 0; i < array.length; i += 1) {
    if (existingNumbers[array[i]] === 1) {
      return true;
    } else {
      existingNumbers[array[i]] = 1;
    }
  }

  return false;
}

Here’s what this function does. It creates an array called existingNumbers, which starts out empty.

Then we use a loop to check each number in the input array. As it encounters each number, it places an arbitrary value (we’ve chosen ...