trees.java

//Build a Tree from its Preorder traversal
public class trees {
    static class Node {
    int data;
    Node left;
    Node right;
    Node(int data) {
    this.data = data;
    this.left = null;
    this.right = null;
    }
    }
    static class BinaryTree {
    static int idx = -1;
    public Node buildTree(int nodes[]) {
    idx++;
    if(nodes[idx] == -1) {
    return null;
    }
    Node newNode = new Node(nodes[idx]);
    newNode.left = buildTree(nodes);
    newNode.right = buildTree(nodes);
    return newNode;
    }
    }
    public static void main(String args[]) {
    int nodes[] = {1, 2, 4, -1, -1, 5, -1, -1, 3, -1, 6, -1, -1};
    BinaryTree tree = new BinaryTree();
    Node root = tree.buildTree(nodes);
    System.out.println(root.data);
    }
}