[LeetCode][JavaScript]Add Binary

Add Binary

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

For example,
a = "11"
b = "1"
Return "100".

https://leetcode.com/problems/add-binary/

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长整型二进制加法。

模拟手工加法的过程，有进位。

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

    var res = "";
    var carry = 0;
    for(var i = 1; i <= a.length; i++){
        var _a = parseInt(a[a.length - i]);
        var _b = parseInt(b[b.length - i]) || 0;
        var add = _a + _b + carry;
        if(add === 3){
            res = "1" + res;
            carry = 1;
        }else if(add === 2){
            res = "0" + res;
            carry = 1;
        }else{
            res = add + res;
            carry = 0;
        }
    }

    if(carry === 1){
        res = "1" + res;
    }
    return res;
};

并不能调自带函数一行搞定，精度不够。

/*
var addBinary = function(a, b) {
    return (parseInt(a, 2) + parseInt(b, 2)).toString(2);
};
*/