public class BinaryTree {
    public TreeNode createTree() {
        TreeNode A = new TreeNode('A');
        TreeNode B = new TreeNode('B');
        TreeNode C = new TreeNode('C');
        TreeNode D = new TreeNode('D');
        TreeNode E = new TreeNode('E');
        TreeNode F = new TreeNode('F');
        TreeNode G = new TreeNode('G');
        TreeNode H = new TreeNode('H');
        A.left = B;
        A.right = C;
        B.left = D;
        B.right = E;
        C.left = F;
        C.right = G;
        E.right = H;
        return A;
    }

    // 前序遍历
    public void preOrderTraversal(TreeNode root){
        if (root==null){
            return;
        }
        System.out.print(root.value+" ");
        preOrderTraversal(root.left);
        preOrderTraversal(root.right);
    }

    // 中序遍历
    public void inOrderTraversal(TreeNode root){
        if (root==null){
            return;
        }
        inOrderTraversal(root.left);
        System.out.print(root.value+" ");
        inOrderTraversal(root.right);
    }

    // 后序遍历
    public void postOrderTraversal(TreeNode root){
        if (root==null){
            return;
        }
        postOrderTraversal(root.left);
        postOrderTraversal(root.right);
        System.out.print(root.value+" ");
    }

    // 遍历思路-求结点个数  前序遍历
    static int size=0;
    public void getSize1(TreeNode root){
        if (root==null){
            return;
        }
        size++;
        getSize1(root.left);
        getSize1(root.right);
    }

    // 子问题思路-求结点个数
    public int getSize2(TreeNode root){
        if (root==null){
            return 0;
        }
        return getSize2(root.left)+getSize2(root.right)+1;
    }

    // 遍历思路-求叶子结点个数
    static int leafSize = 0;
    public void getLeafSize1(TreeNode root){
        if(root == null) {
            return;
        }
        if(root.left == null && root.right == null) {
            leafSize++;
        }
        getLeafSize1(root.left);
        getLeafSize1(root.right);
    }

    // 子问题思路-求叶子结点个数
    public int getLeafSize2(TreeNode root){
        if(root == null) {
            return 0;
        }

        if(root.left == null && root.right == null) {
            return 1;
        }

        return getLeafSize2(root.left) + getLeafSize2(root.right);
    }

    // 子问题思路-求第 k 层结点个数
    public int getKLevelSize(TreeNode root,int k){
        if(root == null) {
            return 0;
        }
        if(k == 1) {
            return 1;
        }
        return getKLevelSize(root.left,k-1) + getKLevelSize(root.right,k-1);
    }

    // 查找 val 所在结点，没有找到返回 null
    // 按照 根 -> 左子树 -> 右子树的顺序进行查找
    // 一旦找到，立即返回，不需要继续在其他位置查找
    public TreeNode find(TreeNode root, char val) {
        if (root == null){
           return null;
       }
        if (root.value==val){
            return root;
        }
        TreeNode ret = find(root.left,val);
        if (ret!=null){
            return ret;
        }
        ret = find(root.right,val);
        if (ret!=null){
            return ret;
        }
        return null;
    }

    // 获取二叉树的高度
    public int getHeight(TreeNode root){
        if (root==null){
            return 0;
        }
        int leftHeight = getHeight(root.left);
        int rightHeight = getHeight(root.right);
        //return  (getHeight(root.left) >  getHeight(root.right) ? getHeight(root.left)+1 :  getHeight(root.right)+1);
        return  (leftHeight >  rightHeight ? leftHeight :  rightHeight)+1;
    }
}