making binary search tree

Question

How do I make a BST when I have an array list of 100 elements like {3,2,6,7,...,99}?

Answer 1

I believe TreeSet is an implementation of a binary search tree. Since integers have a natural ordering you could simply loop through your array of integers and add them all to a TreeSet<Integer>.

Note also, that there is a method Arrays.binarySearch that does a binary search in a sorted array.

int[] someInts = {3,2,6,7, /*...,*/ 99};

// use a TreeSet
TreeSet<Integer> ints = new TreeSet<Integer>();
for (int i : someInts)
    ints.add(i);

System.out.println(ints.contains(2)); // true      
System.out.println(ints.contains(5)); // false

// or sort the array and use Arrays.binarySearch
Arrays.sort(someInts);
System.out.println(Arrays.binarySearch(someInts, 2) >= 0); // true
System.out.println(Arrays.binarySearch(someInts, 5) >= 0); // false

Answer 2

Unless you want to implement everything yourself (in that case, you might want to check here) you should take a look at [Collections.binarySearch][2].

[2]: http://download.oracle.com/javase/1.4.2/docs/api/java/util/Collections.html#binarySearch(java.util.List, java.lang.Object)