Sort an array by boolean value

Hello guys, i hope you are doing really well and trying to solve bigger problems. But sometimes we get really difficult problem to solve in some interviews which can take our valuable chance 😥. Here we will be going through a problem to sort an array by boolean value without using any method and without creating and new array in O(n) time complexity.

This problem was appeared in Amazon interview and i think this will be much useful for you. So let's start 😎 -

Let's assume we have an unsorted array like this -

const response = [
{
id: 1,
name: 'Phone',
isChecked: false
},
{
id: 2,
name: 'Laptop',
isChecked: true
},
{
id: 3,
name: 'Desktop',
isChecked: false
},
{
id: 4,
name: 'Watch',
isChecked: true
}
];

and we need to place all checked items first and unchecked items at last. Below is the code for this.

let lastElementUnchecked;
for (let i = 0; i < response.length; i++) {
    if (response[i].isChecked && lastElementUnchecked !== undefined) {
        let current = response[i];
        response[i] = response[lastElementUnchecked];
        response[lastElementUnchecked] = current;
        i = lastElementUnchecked;
        lastElementUnchecked = undefined;
    } else {
        if (!response[i].isChecked && lastElementUnchecked === undefined) {
            lastElementUnchecked = i;
        }
    }
}

This is very simple example to understand but while interviews it can be tough to reach over.

I hope you like this, thank you for reading 😊

Comments

[Frank Wisniewski]

swap vars:

   [ response[i], response[lastElementUnchecked] ] = 
   [ response[lastElementUnchecked], response[i] ];