338. Counting Bits

// My own solution
class Solution {
public:
    vector<int> countBits(int num) {
        vector<int> ret = {0};
        if(num <= 0) return ret;
        ret.push_back(1);
        int i = 2;
        while(i <= num){
           int start = (i >> 1) - 1;
           int mid = i;
           int end = mid << 1;
           while(++start < mid && i <= num){
               ret.push_back(ret[start]);
               i++;
           }
           mid -= 1;
           while(i < end && i <= num){
               ret.push_back(ret[++mid] + 1);
               i++;
           }
        }
        return ret;
    }
};

// Others' solution
class Solution {
public:
    vector<int> countBits(int num) {
        vector<int> ret(num + 1, 0);
        for(int i = 1; i <= num; i++){  
            ret[i]=ret[i / 2]+(i % 2);  
        }
        return ret;
    }
};