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你學的C是什麼C,你說的++又是什麼++
1
while(sum>0) {
if(sum%2 != 0) {
c++; // counting number of ones
}
sum=sum/2;
}
2
#include <bitset>
#include <iostream>
#include <climits>
size_t popcount(size_t n) {
std::bitset<sizeof(size_t) * CHAR_BIT> b(n);
return b.count();
}
int main() {
std::cout << popcount(1000000);
}
3
#ifdef __APPLE__
#define NAME(name) _##name
#else
#define NAME(name) name
#endif
/*
* Count the number of bits set in the bitboard.
*
* %rdi: bb
*/
.globl NAME(cpuPopcount);
NAME(cpuPopcount):
popcnt %rdi, %rax
ret
/*
* Test if the CPU has the popcnt instruction.
*/
.globl NAME(cpuHasPopcount);
NAME(cpuHasPopcount):
pushq %rbx
movl $1, %eax
cpuid // ecx=feature info 1, edx=feature info 2
xorl %eax, %eax
testl $1 << 23, %ecx
jz 1f
movl $1, %eax
1:
popq %rbx
ret
unsigned cppPopcount(unsigned bb)
{
#define C55 0x5555555555555555ULL
#define C33 0x3333333333333333ULL
#define C0F 0x0f0f0f0f0f0f0f0fULL
#define C01 0x0101010101010101ULL
bb -= (bb >> 1) & C55; // put count of each 2 bits into those 2 bits
bb = (bb & C33) + ((bb >> 2) & C33);// put count of each 4 bits into those 4 bits
bb = (bb + (bb >> 4)) & C0F; // put count of each 8 bits into those 8 bits
return (bb * C01) >> 56; // returns left 8 bits of x + (x<<8) + (x<<16) + (x<<24) + ...
}
unsigned builtinPopcount(unsigned bb)
{
return __builtin_popcountll(bb);
}
3
unsigned int v = value(); // count the number of bits set in v
unsigned int c; // c accumulates the total bits set in v
for (c = 0; v; c++)
{
v &= v - 1; // clear the least significant bit set
}
4
int number = 15; // this is input number
int oneCount = number & 1 ? 1 : 0;
while(number = number >> 1)
{
if(number & 1)
++oneCount;
}
cout << "# of ones :"<< oneCount << endl;
5
int count_1s_in_Num(int num)
{
int count=0;
while(num!=0)
{
num = num & (num-1);
count++;
}
return count;
}
“If you apply the AND operation to the integer and the result of the subtraction, the result is a new number that is the same as the original integer except that the rightmost 1 is now a 0. For example,01110000 AND (01110000 – 1) = 01110000 AND 01101111 = 01100000.This solution has a running time of O(m), where m is the number of 1s in the solution.”
“如果你對減法的結果和一個整數使用與操作,結果會是和原始整數一樣的一個新數,除了最右邊的1此時爲0。結果時間複雜度爲O(m),m爲數中1的個數。”