190. Reverse Bits

Reverse bits of a given 32 bits unsigned integer.
For example, given input 43261596 (represented in binary as 00000010100101000001111010011100), return 964176192 (represented in binary as 00111001011110000010100101000000).
Follow up:If this function is called many times, how would you optimize it?
从n的低位开始一位一位取，取到的是0，result就直接乘2，取到的是1，result就乘2加1。

var reverseBits = function(n) {
    var result = 0;
    var temp = 0;
    for (var i = 0;i < 32;i++) {
         result = result*2;
        if ((n&1)===1)
            result += 1;
        n = n>>1;
    }
    return result;
};