二叉树——二叉树的序列化和反序列化

二叉树的序列化和反序列化
前序遍历的序列化与反序列化

/**
 * Created by Skye on 2018/4/25.
 * 二叉树的序列化和反序列化
 *             0
 *         1        2
 *      3    4    5   6
 *    7  \  / 8  / 9 / \
 */
public class SerializeAndReconstructTree {

    //前序遍历的序列化
    public static String serialBinaryTree(Tree tree){
        if(tree == null) return "#_";

        String res = tree.val + "_";
        res += serialBinaryTree( tree.left );
        res += serialBinaryTree( tree.right );
        return res;
    }

    public static Tree reconstructTree(String str){
        //以分隔符_为标志，将字符串分割为一个一个的结点，组成一个数组
        String []values = str.split("_");

        //队列：用来盛放数组中的字符，这样可以在后面每次出队列一个字符，就省去了使用数组的话，还要有一个额外的指针来指向当前结点
        Queue<String> queue = new LinkedList<>();
        for(int i = 0; i < values.length; i++){
            queue.offer(values[i]);
        }
        return reconstruct(queue);
    }

    public static Tree reconstruct(Queue<String> queue){
        String value = queue.poll();
        if("#".equals(value)){
            return null;
        }
        Tree node = new Tree(Integer.valueOf(value));
        node.left = reconstruct( queue );
        node.right = reconstruct(queue);
        return node;
    }

    public static void inOrder(Tree tree){
        if(tree == null) return;
        
        Stack<Tree> stack = new Stack<>();
        stack.push(tree);
        while(!stack.empty()){
            tree = stack.pop();
            System.out.print(tree.val + " ");
            if(tree.right != null){
                stack.push(tree.right);
            }
            if(tree.left != null){
                stack.push(tree.left);
            }
        }
    }

    public static void main(String[] args){
        Tree tree = new Tree( 0 );
        tree.left = new Tree(1);
        tree.right = new Tree(2);
        tree.left.left = new Tree( 3 );
        tree.left.right = new Tree( 4 );
        tree.left.left.left = new Tree( 7 );
        tree.left.right.right = new Tree(8);
        tree.right.left = new Tree( 5 );
        tree.right.right = new Tree( 6 );
        tree.right.left.right = new Tree( 9 );

        //前序遍历 0 1 3 7 4 8 2 5 9 6
        //中序遍历 7 3 1 4 8 0 5 9 2 6
        //后序遍历 7 3 8 4 1 9 5 6 2 0
        //层序遍历 0 1 2 3 4 5 6 7 8 9
        String serialize = serialBinaryTree( tree );
        System.out.println(serialize);
        Tree root = reconstructTree( serialize );
        inOrder( root );
    }

}