冒泡排序的循环不变量是什么？ (1)do the following N-1 times: (1.1)point to the first element; (1.2)do the following N-1 times: (1.2.1)compare the element pointed to with the next element; (1.2.2)if the compared elements are in the wrong order,exchange them; (1.2.3)point to the next element.冒泡排序的循环不变量是什么？