求整数的位模式中包含几个1

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求整数的位模式中包含几个1。

////#include <iostream>#include <assert.h>#include <algorithm>#include <hash_set>#include <vector>#include <string>#include <assert.h>#include <time.h>using namespace std;// O(n)int bitCount(int x){int sum=0;while (x){x &= (x-1);sum++;}return sum;}// O(logn)int bitCount2(int x){x=((x&0xAAAAAAAA)>>1)+(x&0x55555555);x=((x&0xCCCCCCCC)>>2)+(x&0x33333333);x=((x&0xF0F0F0F0)>>4)+(x&0x0F0F0F0F);x=((x&0xFF00FF00)>>8)+(x&0x00FF00FF);return x;}int main(){int i,x;time_t ib,ie;int N=1000;// bitCountib=clock();while (N--){for (i=0; i<10000; i++){x=bitCount(i);}}ie=clock();cout<<"bitCount: "<<ie-ib<<"  ms"<<endl;// bitCount2N=1000;ib=clock();while (N--){for (i=0; i<10000; i++){x=bitCount2(i);}}ie=clock();cout<<"bitCount: "<<ie-ib<<"  ms"<<endl;// checkfor (i=0; i<50; i++){cout<<i<<" bitCount(i) = "<<bitCount(i)<<" bitCount2(i) = "<<bitCount2(i)<<endl;}return 0;}