函数的作用是：对数组按照键名逆向排序，元素的键名保持不变。
The krsort() function sorts an array by the keys in reverse order. The values keep their original keys.
当你对数组使用选择排序，你选择最小的元素，其余的阵列每一个周期的循环。
When you sort an array using selection sort, you choose the smallest element in the rest of the array on each cycle of the loop.
通过给定的对比方法把数组里面的元素按照升序排序。
Sorts the array's elements in ascending order, as determined by the comparison method specified by a given selector.
不同于其它排序的是，元素不会被放入数组的中任意位置从而推动排序。
Unlike nearly every other sort, items are never written elsewhere in the array simply to push them out of the way of the action.
如果首个元素小于最后一个元素，表明数组是排序的。
Suppose a sorted array is rotated at some pivot unknown to you beforehand.
如果首个元素小于最后一个元素，表明数组是排序的。
Suppose a sorted array is rotated at some pivot unknown to you beforehand.
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