js- offer brush prove safety record title (bit operation)

1. The number of binary 1

My solution

The idea is to start right number is converted to binary representation, with toString () method, and then indexOf to find a record. Then run on vscode, I think rather beautiful, not complement it!

Other analysis

Here involves some basic computer knowledge, this science had forgot, here to record tidy.
The first is the most basic anti-code complement the original code, the following links written very clearly: the original code, anti-code complement Detailed

• It is stored in the computer complement
• Each integer is 4 bytes, 32-bit
• A positive number of the original code, anti-code and complement all the same

Method a: bitwise Analyzing

• The operational definition set binary number n, then:
  when n & 1 = 0, then n binary rightmost one is 0;
  if n & 1 = 1, then n binary rightmost one is 1.

• According to the above description, the following cycle:
  when the number n is not a move to left and right is equal to 0, the end of the cycle;
  n&1 == 1, , count++n the right one.

Question: how do the number n is negative

• Complement the most significant bit is 1 is represented as a negative sign bit.
• n>>1, Signed right, to the left to fill a position, the endless loop;
• n>>>1, Unsigned shift right, 0 to the left to fill the last number n becomes 0.

function NumberOf1(n){
    let count = 0
    let flag = 1
    while(n){
        count +=n&flag
        n = n >>>1
    }
    return count
}

Method two: n & (n-1)
This method is ingenious

• n-1: n binary digits rightmost 1 becomes 0, the 01 on the right have become 1
• n & (n-1): n rightmost binary digit 0 becomes 1, the other bits unchanged
• 1 n number of how many, how many of these operations will be able to do, know the number n becomes 0

function NumberOf1(n){
    let count = 0
    while(n){
        n&=n-1
        count++
    }
    return count
}