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Grokking the Coding Interview Patterns in JavaScript

Counting Bits

Explore how to solve the Counting Bits problem by using dynamic programming to efficiently compute the number of set bits in each number from 0 to n. This lesson helps you understand problem constraints, develop a clear problem-solving approach, and implement your solution in a hands-on coding environment.

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Statement

For a given positive integer, n, your task is to return an array of length n+1n+1 such that for each xx where 0≤x≤n0 \leq x \leq n, result[x] is the count of 11s in the binary representation of xx.

Constraints:

  • 0≤n≤1040 \leq n \leq 10^4

Examples

Understand the problem

Let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps you check if you’re solving the correct problem:

Counting Bits

1.

What will be the output if n=6n = 6?

A.

[0,1,1,2,1,2,2][0, 1, 1, 2, 1, 2, 2]

B.

[0,1,1,2,1,1,2][0, 1, 1, 2, 1, 1, 2]

C.

[0,1,2,2,1,2,1][0, 1, 2, 2, 1, 2, 1]

1 / 4

Figure it out!

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Sequence - Vertical
Drag and drop the cards to rearrange them in the correct sequence.
1
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Try it yourself

Implement your solution in the following coding playground.

JavaScript
usercode > main.js
function countingBits(n) {



    // Replace this placeholder return statement with your code

    return [];

}



export { countingBits };
Counting Bits