【Java】创建二叉树，从上至下打印二叉树

电玩女神 2022-11-11 10:50 178阅读 0赞

/** * 二叉树的生成 */
    
    
        public static ArrayList<ArrayList<Object>> PrintFromTopToBottom(TreeNode root) { 
            Queue<TreeNode> queue = new LinkedList<>();
            ArrayList<ArrayList<Object>> ret = new ArrayList<>();
    
            queue.add(root);
            while (!queue.isEmpty()) { 
                int cnt = queue.size();
                ArrayList<Object> arr = new ArrayList<>();
                while (cnt-- > 0) { 
                    TreeNode t = queue.poll();
    // if (t == null || t.data.equals("#"))
    // continue;
    
                    arr.add(t.data);
    
                    queue.add(t.left);
                    queue.add(t.right);
                }
    
                if (arr.size() != 0)
                    ret.add(arr);
            }
            return ret;
        }
    
    
        static class TreeNode { 
            Object data;
            TreeNode left;
            TreeNode right;
    
            public TreeNode() { 
            }
    
            public TreeNode(Object data, TreeNode left, TreeNode right) { 
                this.data = data;
                this.left = left;
                this.right = right;
            }
        }
    
        public static TreeNode arrayToBTree(Object[] arrs) { 
    
            List<TreeNode> nodes = new ArrayList<>(arrs.length);
            for (Object obj : arrs) { 
                TreeNode treeNode = new TreeNode();
                treeNode.data = obj;
                nodes.add(treeNode);
            }
    
            for (int i = 0; i < arrs.length/2 - 1; i++) { 
                TreeNode node = nodes.get(i);
                node.left = nodes.get(i*2 + 1);
                node.right = nodes.get(i*2 + 2);
            }
            // 只有当总节点数是奇数时，最后一个父节点才有右子节点
            int lastPNodeIndex = arrs.length/2 - 1;
            TreeNode lastPNode = nodes.get(lastPNodeIndex);
            lastPNode.left = nodes.get(lastPNodeIndex*2 + 1);
            if (arrs.length%2 != 0) { 
                lastPNode.right = nodes.get(lastPNodeIndex*2 + 2);
            }
    
            return nodes.get(0);
        }