A C# solution.

  • 1
    public class Solution {
        public int[] CountBits(int num) {
            int[] counts = new int[num+1];
            for(int i = 1; i < counts.Length; i++)
                counts[i] = counts[i/2] + (i % 2);
            return counts;

  • 1

    This is the best solution I've seen so far. But, I am not able to figure out what approach would lead to this solution. What was your thought process?

    Edit 1: I see what's going on. Bit-shifting to the left doubles the number, keeping the number of 1s the same. If its an odd number, just add one more bit to the end with (i % 2). Brilliant!

    Edit 2: Just saw the top voted answer too. Exact same concept, implemented with bit manipulation.

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