10. The number of binary 1

10. The number of binary 1

Algorithm Description

An integer that indicates the number of the output of the binary number 1 in. Wherein a negative number indicates a complement.

Problem-solving ideas

Solution 1: May cause an infinite loop of solution

N 1 and the number of input and computation done, left 1 bit are 0, and the operation result is 0 do; the result is 0 or 1 depends on the last one is 0 or 1

Enter n	1	0	1	0	1
1	0	0	0	0	1
result	0	0	0	0	1

The main problem lies in the n >> 1above negative is left up to the left 1, resulting in an infinite loop

function NumberOf1(n)
{
    // write code here
    var count = 0;
    while (n) {
       if (n & 1)
         count ++;
       n = n >> 1;
    }
    return count;
}

Solution 2: General Solution

The 1left one, and the n-done operation, 32-bit binary number 0 into the left 32

Enter n	1	0	1	0	1
1	0	0	1	0	0
result	0	0	1	0	0

function NumberOf1(n)
{
    // write code here
    var count = 0;
    var i = 1;
    while (i) {
       if (n & i)
         count ++;
       i = i << 1;
    }
    return count;
}

Solution 3: optimal solution

Discover the laws for binary numbers ①, ② after it by -1, then ① and ② do with the operation, the result of a less just 1

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//.js
function NumberOf1(n)
{
    // write code here
    //不等于0
    var count = 0;
    while(n) {
        count ++;
        n = n & (n - 1);
    }
    return count;
}

//.java
public class Solution {
    public int NumberOf1(int n) {
        int count = 0;
        while (n != 0) {
            count++;
            n = n & (n - 1);
        }
        return count;
    }
}