338. Counting Bits(Dynamic Programming, Bit Manipulation)***

문제

Given an integer n, return an array ans of length n + 1 such that for each i (0 <= i <= n), ans[i] is the number of 1's in the binary representation of i.

https://leetcode.com/problems/counting-bits/description/

Example 1:

Input: n = 2
Output: [0,1,1]
Explanation:
0 --> 0
1 --> 1
2 --> 10

Example 2:

Input: n = 5
Output: [0,1,1,2,1,2]
Explanation:
0 --> 0
1 --> 1
2 --> 10
3 --> 11
4 --> 100
5 --> 101

풀이

class Solution {
    public int[] countBits(int n) {
        int[] res = new int[n+1];
        int j = 1;

        for(int i = 1; i < n+1; i++){
            if(j*2 == i) j *= 2;

            res[i]=res[i-j]+1;
        }

        return res;
    }
}

참고

https://leetcode.com/problems/counting-bits/solutions/79557/how-we-handle-this-question-on-interview-thinking-process-dp-solution/?orderBy=most_votes