常规的交换

var a = 11;
var b = 12;
var temp;//额外的变量
temp = a;
a = b;
b = temp;

不使用额外空间

var a = 11;
var b = 12;
a = a+b;//和
b = a-b;//a
a = a-b;//b

二进制操作，高效

var a = 11;
var b = 12;
a = a^b;
b = a^b;//a^b^b = a本身
a = a^b;//(a^b)^(a^b^b) = a^b^a = b本身