Leetcode 338. Counting Bits

题目·：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.

思路：对于前n为的数如果已经统计了，假设结果保存在vector<int> re里面，那第n+1为所对应的应该为re[0~end]依次加一。比如三位的数，每个前面加上个1就可以组成第四位的；第二位的数第三位为0，第一位为1页是组成第四位的。依次相加，直到结果数为num+1为止。

class Solution {public:    vector<int> countBits(int num) {        vector<int> re;        int count1=1;        re.push_back(0);        while(1){            if(re.size()==num+1) return re;            for(int i=0;i<=count1-1;i++) {                re.push_back(re[i]+1);                if(re.size()==num+1) return re;            }            count1*=2;        }    }};

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