Less or Equal
题意翻译
给你一个长度为n(1≤n≤2⋅10^5),由整数组成的数组a(1≤ai≤10^9),一个整数k(0≤k≤n)。\
找到一个整数x,1≤x≤10^9 。要求数组a中有k个小于等于x的数。\
找到则输出x,否则输出-1。
题目描述
You are given a sequence of integers of length $ n $ and integer number $ k $ . You should print any integer number $ x $ in the range of $ [1; 10^9] $ (i.e. $ 1 \le x \le 10^9 $ ) such that exactly $ k $ elements of given sequence are less than or equal to $ x $ .
Note that the sequence can contain equal elements.
If there is no such $ x $ , print "-1" (without quotes).
输入输出格式
输入格式
The first line of the input contains integer numbers $ n $ and $ k $ ( $ 1 \le n \le 2 \cdot 10^5 $ , $ 0 \le k \le n $ ). The second line of the input contains $ n $ integer numbers $ a_1, a_2, \dots, a_n $ ( $ 1 \le a_i \le 10^9 $ ) — the sequence itself.
输出格式
Print any integer number $ x $ from range $ [1; 10^9] $ such that exactly $ k $ elements of given sequence is less or equal to $ x $ .
If there is no such $ x $ , print "-1" (without quotes).
输入输出样例
输入样例 #1
7 4
3 7 5 1 10 3 20
输出样例 #1
6
输入样例 #2
7 2
3 7 5 1 10 3 20
输出样例 #2
-1
说明
In the first example $ 5 $ is also a valid answer because the elements with indices $ [1, 3, 4, 6] $ is less than or equal to $ 5 $ and obviously less than or equal to $ 6 $ .
In the second example you cannot choose any number that only $ 2 $ elements of the given sequence will be less than or equal to this number because $ 3 $ elements of the given sequence will be also less than or equal to this number.