[Interview questions] wins the Offer-10- statistical binary number 1

Topic Overview

Implement a function, asks an integer, the number of output binary number corresponding to the number of 1 in. 9 example is represented as a binary 1001, then the input 9, then, the screen printing 2

Solving Method 1

size_t numberOf1(int value)
{
	int count = 0;
	
	while(value){
		if(value & 0x01){
			++count;
		}
		value = value >> 1;
	}
	
	return count;
}

Analysis:
One problem with this method encountered is negative, a -1 if passed, what would happen?
Yes, infinite loop , we need to improve.

Solving Method 2

//防止出现负数导致无线循环
size_t numberOf1(int value)
{
	int count = 0;
	
	for(size_t i = 0; i < 32; ++i){
		if(value % 1){
			++count;
		}
		value = value >> 1;
	}
	return count;
}

Analysis:
negative number may be calculated, but every time cycle 32 times, can not be optimized a little bit?

Solving Method 3

//当一个数与上比自己小1的数，那么该数最后一个1会被置为0
size_t numberOf1(int value)
{
	int count = 0;
	
	while(value){
		++count;
		value = (value - 1) & value;
	}	
	
	return count;
}

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Original link: https://blog.csdn.net/qq_31828515/article/details/62041384
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