A Common-Sense Guide to Data Structures and Algorithms, Second Edition, 2nd Edition

A Practical Example

Suppose you are writing a JavaScript application, and somewhere in your code you find that you need to get the intersection between two arrays. The intersection is a list of all the values that occur in both of the arrays. For example, if you have the arrays, [3, 1, 4, 2] and [4, 5, 3, 6], the intersection would be a third array, [3, 4], since both of those values are common to the two arrays.

Here’s one possible implementation:

function intersection(firstArray, secondArray){
    let result = [];

    for (let i = 0; i < firstArray.length; i++) {
        for (let j = 0; j < secondArray.length; j++) {
            if (firstArray[i] == secondArray[j]) {
                result.push(firstArray[i]);
            }
        }
    }
    return result;
}

Here, we are ...