Implementing Priority Sort in JavaScript

We are required to write a JavaScript function that takes in two arrays of numbers, second being smaller in size than the first.

Our function should return a sorted version of the first array (in increasing order) but put all the elements that are common in both arrays to the front.

For example ? If the two arrays are ?

const arr1 = [5, 4, 3, 2, 1];
const arr2 = [2, 3];

Then the output should be ?

[2, 3, 1, 4, 5]

How It Works

The priority sort algorithm works by using a custom comparator function that:

• Prioritizes elements that exist in the priority array (arr2)
• Maintains ascending order for non-priority elements
• Uses the native JavaScript sort() method with custom logic

Implementation

const arr1 = [5, 4, 3, 2, 1];
const arr2 = [2, 3];

// helper function
const sorter = (a, b, arr) => {
    if(arr.includes(a)){
        return -1;
    };
    if(arr.includes(b)){
        return 1;
    };
    return a - b;
};

const prioritySort = (arr1, arr2) => {
    arr1.sort((a, b) => sorter(a, b, arr2));
};

prioritySort(arr1, arr2);
console.log(arr1);

[ 2, 3, 1, 4, 5 ]

Alternative Approach: Separate and Combine

Another way to implement priority sort is by separating priority and non-priority elements:

const prioritySortAlternative = (arr1, arr2) => {
    const priority = arr1.filter(item => arr2.includes(item)).sort((a, b) => a - b);
    const nonPriority = arr1.filter(item => !arr2.includes(item)).sort((a, b) => a - b);
    return [...priority, ...nonPriority];
};

const arr1 = [5, 4, 3, 2, 1];
const arr2 = [2, 3];

const result = prioritySortAlternative(arr1, arr2);
console.log(result);

[ 2, 3, 1, 4, 5 ]

Comparison

Conclusion

Priority sort allows you to maintain order while giving precedence to specific elements. The custom sorter approach modifies the original array, while the separate-and-combine method preserves it and returns a new sorted array.