public class BinaryTree {
    static class Node {
        String value;
        Node leftTree, rightTree;
        public Node(String value, Node leftTree, Node rightTree) {
            this.value = value;
            this.leftTree = leftTree;
            this.rightTree = rightTree;
        }
        void printValue() {
            System.out.print(value);
        }
    }
    public static Node createNode(String value) {
        return new Node(value, null, null);
    }
    public static Node createNode(char value) {
        return createNode(String.valueOf(value));
    }
    /**
     * 添加节点到左子树
     */
    public static void addNodeToLeft(Node root, Node child) {
        if (root.leftTree == null) {
            root.leftTree = child;
        } else {
            throw new RuntimeException("the left child has already created");
        }
    }
    /**
     * 添加节点到右子树
     */
    public static void addNodeToRight(Node root, Node child) {
        if (root.rightTree == null) {
            root.rightTree = child;
        } else {
            throw new RuntimeException("the right child has already created");
        }
    }
    /**
     * 先序遍历
     */
    public static void preorder_visit(Node root) {
        root.printValue();
        if (root.leftTree != null) {
            preorder_visit(root.leftTree);
        }
        if (root.rightTree != null) {
            preorder_visit(root.rightTree);
        }
    }
      
    /**
     * 中序遍历
     */
    public static void inorder_visit(Node root) {
        if (root.leftTree != null) {
            inorder_visit(root.leftTree);
        }
        root.printValue();
        if (root.rightTree != null) {
            inorder_visit(root.rightTree);
        }
    }
      
    /**
     * 后序遍历
     */
    public static void posorder_visit(Node root) {
        if (root.leftTree != null) {
            posorder_visit(root.leftTree);
        }
        if (root.rightTree != null) {
            posorder_visit(root.rightTree);
        }
        root.printValue();
    }
      
    /**
     * 根据前序和中序来创建这棵树
     */
    public static Node createTreeByPreAndIn(Node root, String pre_values,
            String in_values) {
        if (!"".equals(in_values)) {
              
            String new_pre_values = synchronizedPreAndIn(pre_values,in_values);//同步先序和中序字符串
              
            char rootValue = new_pre_values.charAt(0);//这样可以保证，先序的第一个肯定是这棵树的根节点
            root = createNode(rootValue);
            int rootIndexOfIn = in_values.indexOf(rootValue);//得到根节点在中序中的位置
              
            String leftInValues = in_values.substring(0,rootIndexOfIn);//节点左边的一大串
            String rightInvalues = in_values.substring(rootIndexOfIn+1,in_values.length());//节点右边的一大串
            /**
             * 如果右边一大串就剩下一个了，说明这肯定就是这课树的右节点,如果还剩下多个就继续递归调用
             */
            if(leftInValues.length() == 1){
                addNodeToLeft(root, createNode(leftInValues));
            }else if(leftInValues.length() != 0){
                addNodeToLeft(root, createTreeByPreAndIn(root, new_pre_values, leftInValues));
            }
              
            /**
             * 如果左边一大串就剩下一个了，说明这肯定就是这课树的左节点,如果还剩下多个就继续递归调用
             */
            if(rightInvalues.length() == 1){
                addNodeToRight(root, createNode(rightInvalues));
            }else if(rightInvalues.length() != 0){
                addNodeToRight(root, createTreeByPreAndIn(root, new_pre_values, rightInvalues));
            }
        }
        return root;
    }
    /**
     * 每次都把在pre_values但是不在in_values里面的元素删掉，但是顺序不要变
     */
    private static String synchronizedPreAndIn(String preValues, String inValues) {
          
        String retVal = "";
          
        for (int i = 0; i < preValues.length(); i++) {
            for (int j = 0; j < inValues.length(); j++) {
                if(preValues.charAt(i) == inValues.charAt(j)){
                    retVal+=preValues.charAt(i);
                }
            }
        }
          
        return retVal;
    }
    public static void main(String[] args) {
        Node a = createTreeByPreAndIn(null, "ADCEFGHB", "CDFEGHAB");
          
        /*Node a = createNode("A");
        Node b = createNode("B");
        Node c = createNode("C");
        Node d = createNode("D");
        Node e = createNode("E");
        Node f = createNode("F");
        Node g = createNode("G");
        Node h = createNode("H");
          
        addNodeToLeft(a, d);
        addNodeToRight(a, b);
        addNodeToLeft(d, c);
        addNodeToRight(d, e);
        addNodeToLeft(e, f);
        addNodeToRight(e, g);
        addNodeToRight(g, h);*/
          
        System.out.print("先序遍历：");
        preorder_visit(a);
        System.out.println();
          
        System.out.print("中序遍历：");
        inorder_visit(a);
        System.out.println();
          
        System.out.print("后序遍历：");
        posorder_visit(a);
        System.out.println();  
    }
}