第k小元素（分治法） 给定一个线性序列集，要求求出其中指定的第K小的数的值和位置.如给定n个元素和一个整数i，1≤i≤n，输出这n个元素中第i小元素的值及其位置；-First k small element (divide and conquer) Given a set of linear sequence, where the specified requirements determined the K value and the small number of locations, such as a given n elements and an integer i, 1 ≤ i ≤ n, output this is the n elements of the i-th element value and the position of the small