476. Number Complement

Given a positive integer, output its complement number. The complement strategy is to flip the bits of its binary representation.

Note:

1. The given integer is guaranteed to fit within the range of a 32-bit signed integer.
2. You could assume no leading zero bit in the integer’s binary representation.

Example 1:

Input: 5
Output: 2
Explanation: The binary representation of 5 is 101 (no leading zero bits), and its complement is 010. So you need to output 2.

Example 2:

Input: 1
Output: 0
Explanation: The binary representation of 1 is 1 (no leading zero bits), and its complement is 0. So you need to output 0.

/**
 * @param {number} num
 * @return {number}
 */
var findComplement = function(num) {
    // convert num to string in binary
    var s= num.toString(2);
    // swap 1,0
    var q = s.replace(/1/g, 'a');
    var p = q.replace(/0/g, 'b');
    
    p = p.replace(/b/g, 1);
    p = p.replace(/a/g, 0);
    /*
    convert binary string to decimal
    var digit = parseInt(binary, 2);
    */
   
    var digit = parseInt(p, 2);
    return digit;
};

思路：

先轉二進制

在交換01

(利用 ab 分別取代 10 接著用 01 把 ab 取代回來)

再轉回去十進制

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/parseInt

Syntax

parseInt(string, radix);