leetcode 338. Counting Bits

Given a non negative integer number num. For every numbers i in the range 0 ≤ i ≤ num calculate the number of 1's in their binary representation and return them as an array.

Example:
For num = 5 you should return [0,1,1,2,1,2].

class Solution {
public:
    vector<int> countBits(int num) {
        vector<int> result(num + 1, 0);
        for(int i = 1; i <= num; i++) {
            // 发现i的变化规律
            result[i] = result[i & (i - 1)] + 1;
        }
        return result;
    }
};

呼呼呼山(http://code4fun.me)
2 May 2017 7:05 PM