Java，TreeSet。 我们可以从第一个元素开始迭代元素吗？

Question

Good day.

I use TreeSet , for example TreeSet<Integer> t . And I want to print all numbers from set t between x and y.

void print(Integer x,Integer y, TreeSet<Integer> t){
...
}

How to do it? Of Course I can get t.iterator() , and iterator all numbers from set and check is it greats x and less y. Time complexity is y steps. but if yx is small. It will be better to get t.higher() and after that iterate the elements in set until it less than y. This solution can be implemented in C++. And it's time complexity is log (t.size())+(yx) .

How to do in in Java?

Answer 1

You can use the SortedSet interface (which TreeSet implements). For example:

SortedSet<Integer> set = new TreeSet<Integer>();

for (int i = 1; i <= 5; ++i) {
    set.add(i);
}

int from = 2;
int to = 4;
for (int x : set.subSet(from, to+1)) { // Note that the higher bound is exclusive.
    System.out.println(x);
}

Output:

2
3
4