2.add-binary.md

Add Binary

Given two binary strings, return their sum (also a binary string).

The input strings are both `non-empty` and contains only characters `1` or `0`.

Example 1:

Input: a = "11", b = "1"
Output: "100"

Example 2:

Input: a = "1010", b = "1011"
Output: "10101"

JavaScript

/**
 * @param {string} a
 * @param {string} b
 * @return {string}
 */
var addBinary = function (a, b) {
    var aLength = a.length;
    var bLength = b.length;

    if (aLength < bLength) {
        var dif = bLength - aLength;
        var concatString = "";
        while (dif) {
            --dif;
            concatString += "0";
        }
        a = concatString + a;
    } else if (aLength > bLength) {
        var dif = aLength - bLength;
        var concatString = "";
        while (dif) {
            --dif;
            concatString += "0";
        }
        b = concatString + b;
    }

    var length = a.length;
    var result = '';
    var rememeber = 0;

    for (var i = length - 1; i >= 0; --i) {
        var slug = ((+a[i]) + (+b[i]) + rememeber);
        if (slug >= 2) {
            slug = slug - 2;
            rememeber = 1;
        } else {
            rememeber = 0;
        }
        result = slug + result;
    }

    if (rememeber === 1) {
        result = "1" + result;
    }

    return result;
};

PHP

<?php
function addBinary(string $a, string $b): string
{
    $aCount = strlen($a);
    $bCount = strlen($b);

    if ($aCount < $bCount) {
        $diff = $bCount - $aCount;
        $concatString = '';
        while ($diff) {
            $concatString = '0' . $concatString;
            --$diff;
        }
        $a = $concatString . $a;
    } elseif ($aCount > $bCount) {
        $diff = $aCount - $bCount;
        $concatString = '';
        while ($diff) {
            $concatString = '0' . $concatString;
            --$diff;
        }
        $b = $concatString . $b;
    }

    $count = strlen($a);
    $remember = 0;
    $result = '';

    for ($i = $count - 1; $i >= 0; --$i) {
        $slug = $a[$i] + $b[$i] + $remember;
        if ($slug >= 2) {
            $slug = $slug - 2;
            $remember = 1;
        } else {
            $remember = 0;
        }
        $result = $slug . $result;
    }

    if ($remember === 1) {
        $result = '1' . $result;
    }

    return $result;
}

var_dump(addBinary('11','1'));