关于二叉树深度 和 高度的问题

根节点的高度 = 最大深度 ( 后序遍历 )

104.二叉树的最大深度

public int maxDepth(TreeNode root) {
        return getDepth(root);
    }

public int getDepth(TreeNode cur) {
        if (cur == null) return 0;
        int leftDepth = getDepth(cur.left);
        int rightDepth = getDepth(cur.right);
        return 1 + Math.max(leftDepth, rightDepth);
    }
    
 //通过队列做
 
    public int maxDepthByDeque(Node root) {
        Deque<Node> deque = new LinkedList<>();
        if (root == null) return 0;
        deque.offerLast(root);
        Node cur;
        int depth = 0;
        while (!deque.isEmpty()) {
            int len = deque.size();
            while (len > 0) {
                cur = deque.pollFirst();
                for (Node child : cur.children) {
                    deque.offerLast(child);
                }
                len--;
            }
            depth++;
        }
        return depth;
    }

111.二叉树的最小深度

    public int minDepth(TreeNode root) {
        return getMinDepth(root);
    }
    public int getMinDepth(TreeNode cur) {
        if (cur == null) {
            return 0;
        }
        // 下面可以简化,很简单,吧leftDepth换成对应的函数
        // 为了看动,不简化.
        int leftDepth = getMinDepth(cur.left);
        int rightDepth = getMinDepth(cur.right);
        if (cur.right == null && cur.left != null) {
            return 1 + leftDepth;
        }
        if (cur.left == null && cur.right != null) {
            return 1 + rightDepth;
        }
        return 1 + Math.min(leftDepth, rightDepth);
    }

222. 完全二叉树的节点个数

public int countNodes(TreeNode root) {
        if (root == null) {
            return 0;
        }
//        加入下面这一整块,就是为了利用完全二叉树的性质 -> 完全二叉树节点数: 2^n-1(n=depth)
//        TreeNode leftTree = root, rightTree = root;
//        int rightDepth = 0, leftDepth = 0;
//        while (rightTree.right != null) {
//            rightDepth++;
//            rightTree = rightTree.right;
//        }
//        while (leftTree.left != null) {
//            leftDepth++;
//            leftTree = leftTree.left;
//        }
//        if (leftDepth == rightDepth) {
//            return 1 << leftDepth + 1;
//        }
//		上面注释全部删除,或者全部加入,都可以运行成功
        int right = countNodes(root.right);
        int left = countNodes(root.left);
        return left + right + 1;
    }