算法导论练习2.3-7：请给出一个运行时间为Θ(nlgn)的算法，使之能在给定一个由n个整数构成的集合S和另一个整数x时，判断出S中是否存在有两个其和等于x的元素。-Introduction to Algorithms Exercise 2.3-7: Please give a running time of Θ (nlgn) algorithm, so that it can in the given form by a set of n integers S and another integer x, determine whether there is S x is equal to two of its elements.