https://www.codewars.com/kata/5672682212c8ecf83e000050/java
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Consider a sequence u where u is defined as follows:
- The number u(0) = 1 is the first one in u.
- For each x in u, then y = 2 * x + 1 and z = 3 * x + 1 must be in u too.
- There are no other numbers in u.
<html />Ex: u = [1, 3, 4, 7, 9, 10, 13, 15, 19, 21, 22, 27, ...]
1 gives 3 and 4, then 3 gives 7 and 10, 4 gives 9 and 13, then 7 gives 15 and 22 and so on...
1. Task:
Given parameter n the function dbl_linear (or dblLinear...) returns the element u(n) of the ordered (with <) sequence u (so, there are no duplicates).
2. Example:
<html />dbl_linear(10) should return 22
3. Note:
Focus attention on efficiency
3.0.1. Solution
: idea는 set과 Treeset을 이용하는 것
: 계속해서 첫 요소를 지워가는 것
<java />
import java.util.SortedSet;
import java.util.TreeSet;
class DoubleLinear {
public static final int FIRST_NUM = 1;
public static int dblLinear (int n) {
int first = FIRST_NUM;
SortedSet<Integer> list = new TreeSet<>();
list.add(first);
for(int i = 0; i<n; i++) {
list.add(function1(list.first()));
list.add(function2(list.first()));
list.remove(list.first());
}
return list.first();
}
private static Integer function1(Integer a) { return (2*a)+1; }
private static Integer function2(Integer b) { return (3*b)+1; }
}
