Count how many 1 in binary representation of a 32-bit integer.
Given 32, return 1
Given 5, return 2
Given 1023, return 9
If the integer is n bits with m 1 bits. Can you do it in O(m) time?
常规解法：
class Solution { public: /** * @param num: an integer * @return: an integer, the number of ones in num */ int countOnes(int num) { // write your code here int cnt = 0; while(num != 0){ cnt += (num&1); num >>= 1; } return cnt; } };
使用STL的解法：
#include <bitset> class Solution{ public: /** * @param num: an integer * @return: an integer, the number of ones in num */ int countOnes(int num) { // write your code here bitset<sizeof(int)*8> bitvec(num); return bitvec.count(); } };
原文：http://www.cnblogs.com/changchengxiao/p/4731863.html