算法题---二叉树层序遍历

二叉树层序遍历:

    class TreeNode {
        TreeNode left;
        TreeNode right;
        int value;
    }

 void levelTraversal(TreeNode root) {
        Queue<TreeNode> q = new LinkedList<>();
        q.add(root);
        while (!q.isEmpty()) {
            TreeNode nowNode = q.poll();
            if (nowNode != null) {
                System.out.println(nowNode.value + " ");
                //添加数据节点
                if (nowNode.left != null) {
                    //如果左子节点不为null,则将子节点加入队列
                    q.add(nowNode.left);
                }
                if (nowNode.right != null) {
                    //如果右子节点不为null,则将子节点加入队列
                    q.add(nowNode.right);
                }
            }
        }
    }

 

求二叉树的最大深度：

  int treeDepth(TreeNode root) {
        Queue<TreeNode> q = new LinkedList<>();
        q.add(root);
        int depth = 0, count = 0, currentLevelCount = 1;  //nextcount为该层应有的节点个数
        while (!q.isEmpty()) {
            TreeNode nowNode = q.poll();
            count++;
            if (nowNode != null) {
                System.out.println(nowNode.value + " ");
                //添加数据节点
                if (nowNode.left != null) {
                    //如果左子节点不为null,则将子节点加入队列
                    q.add(nowNode.left);
                }
                if (nowNode.right != null) {
                    //如果右子节点不为null,则将子节点加入队列
                    q.add(nowNode.right);
                }

                if (count == currentLevelCount) { //此时该层已经遍历完，队列中的元素应为下一层结点个数
                    depth++;
                    count = 0;
                    currentLevelCount = q.size();
                }
            }
        }
        return depth;
    }

    //递归版本
    public int TreeDepth(TreeNode root) {
        if (root == null) return 0;
        int nLeft = TreeDepth(root.left);
        int nRight = TreeDepth(root.right);
        return (nLeft > nRight) ? (nLeft + 1) : (nRight + 1);
    }