First clear solution for [old] Binary Count by Sim0000 - javascript coding challenges

Enable Javascript in your browser and then refresh this page, for a much enhanced experience.

First solution in Clear category for [old] Binary Count by Sim0000

"use strict";

function binaryCount(number){
    for(var n = 0; number != 0; number &= number - 1) n++;
    return n;
}


var assert = require('assert');

if (!global.is_checking) {
    assert.equal(binaryCount(4), 1);
    assert.equal(binaryCount(15), 4);
    assert.equal(binaryCount(1), 1);
    assert.equal(binaryCount(1022), 9);
    console.log("Coding complete? Click 'Check' to review your tests and earn cool rewards!");
}

Sept. 21, 2016

Comments:

movieclip on Oct. 6, 2016, 6:22 a.m.
Brilliant!

jdent on Jan. 8, 2017, 9:03 p.m.
Wow, this one converges very fast. Did you come up with it on your own?

Sim0000 on Jan. 9, 2017, 8:43 a.m.
Thank you. It is not my original. My memory is ambiguous. I knew at least since the 1980's.

vlikin_62f1ecf1e2974c5baeac5f0 on June 25, 2018, 10:42 a.m.
I see that this is an old style. This is very cool - specific for loop configuration :) I could not understand the main idea. number - 1

Sim0000 on June 25, 2018, 10:39 p.m.
We can clear the least 1 bit by x &= x - 1. For example, x = 5. In binary, x & (x - 1) is 101 & 100 == 100. Another example, x = 6, 110 & 101 == 100. x = 12, 1100 & 1011 == 1000. Lets think what x - 1 means. When x has 1 at bit position n, x - 1 has 0 at bit n and 1 at from bit (n - 1) to bit 0. In another word, from bit n to bit 0 of x - 1 is inverted from x. I hope this may help you :-)

vlikin_62f1ecf1e2974c5baeac5f0 on June 26, 2018, 1:07 p.m.
I see. It is a solution that implements shifting. Could it be something with the shifting operator? >>>

Sim0000 on June 27, 2018, 7:44 a.m.
We can also solve this problem by using shift operator. But above method is more efficient, because loop count is hamming weight of data :-)

megaexception on Feb. 1, 2019, 5:04 a.m.
i've tried to do this with shifting operators, but run into a fact that in javascript binary operators are limited to 32 bits, so you cannot count bits for numbers larger than that this solution will work with any integral number possible. it's really cool.

No Station

WebStorm The smartest JavaScript IDE. WebStorm is a powerful JavaScript IDE that makes you productive. Try free!