我有以下程序。
import java.util.*;
public class Solution {
public static <U extends Number> double median(List<U> l) {
double Q = 0;
int n = l.size();
if (n%2 == 0) {
Q = ((int)l.get(n/2) + (int)l.get(n/2-1)) / (double)2;
} else {
Q = new Double((int)l.get(n/2));
}
return Q;
}
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int n = sc.nextInt();
List<Integer> l = new ArrayList<>();
for (int i = 0; i < n; i++){
l.add(sc.nextInt());
}
Collections.sort(l);
double Q1 = 0, Q2 = 0, Q3 = 0;
List<Integer> lower = new ArrayList<>();
List<Integer> upper = new ArrayList<>();
if (n%2 == 0) {
lower.addAll(l.subList(0, n/2));
upper.addAll(l.subList(n/2, n));
} else {
lower.addAll(l.subList(0, n/2));
upper.addAll(l.subList(n/2 + 1, n));
}
Q2 = median(l);
Q1 = median(lower);
Q3 = median(upper);
System.out.format("%.0f%n", Q1);
System.out.format("%.0f%n", Q2);
System.out.format("%.0f%n", Q3);
sc.close();
}
}
当我尝试从eclipse运行它时,它编译得很好并在我的本地机器上运行,但是当我将它提交给hackerrank时,我得到以下编译错误。
Solution.java:12: error: incompatible types: U cannot be converted to int
Q = ((int)l.get(n/2) + (int)l.get(n/2-1)) / (double)2;
^
where U is a type-variable:
U extends Number declared in method <U>median(List<U>)
Solution.java:12: error: incompatible types: U cannot be converted to int
Q = ((int)l.get(n/2) + (int)l.get(n/2-1)) / (double)2;
^
where U is a type-variable:
U extends Number declared in method <U>median(List<U>)
Solution.java:14: error: incompatible types: U cannot be converted to int
Q = new Double((int)l.get(n/2));
^
where U is a type-variable:
U extends Number declared in method <U>median(List<U>)
3 errors
我甚至不理解为什么我必须将每个列表元素强制转换为int,我认为因为U扩展了Number,所以我应该能够添加列表元素而不会返回int。有什么我不了解仿制药吗? Q1,Q2,Q3保证是整数(但这仅仅是因为输入测试用例),但这不重要,为什么我的程序编译不正确?
答案 0 :(得分:0)
如果你将列表项强制转换为整数,为什么要将中值方法声明为泛型?
将其更改为docker run -itd -p 5432:5432 --name postgres_test -v /path/in/your/host :/path/in/your/container postgres_test psql -h 192.168.99.100 -p 5432 -U pguser -W pgdb
并将所有转换删除为int。
答案 1 :(得分:0)
您可以在intValue()
元素上调用Number
方法,而不是将它们转换为int。
(https://docs.oracle.com/javase/8/docs/api/java/lang/Number.html#intValue--)