LeetCode 338. Counting Bits

https://leetcode.com/problems/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].

Follow up: 

• It is very easy to come up with a solution with run time O(n*sizeof(integer)). But can you do it in linear time O(n) /possibly in a single pass?
• Space complexity should be O(n).
• Can you do it like a boss? Do it without using any builtin function like __builtin_popcount in c++ or in any other language.

 

• vector - C++ Reference
  • 　　http://www.cplusplus.com/reference/vector/vector/?kw=vector
• 二分分治。捡起vector用法。。。

#include <iostream>
#include <vector>
using namespace std;

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

int main ()
{
    Solution testSolution;
    vector<int> result(5, 0);
    
    result = testSolution.countBits(5);    

    for (int i = 0; i < result.size(); i ++)
        cout << result[i] << endl;

    char ch;
    cin >> ch;
    
    return 0;
}