### 打印二叉树  ~~~ // 打印二叉树，基于中序遍历顺序加节点层级构建二维数组实现打印 public static void printTree(TreeNode node){ List<TreeNode> inList = getInList(node); Map<TreeNode,Integer> levelMap = new HashMap<>(); int level = handleTreeLevel(levelMap,node); // 以中序遍历顺序构建二维数组 int row = level; int col = (int) Math.pow(2,row)-1; int[][] nums = new int[row][col]; for(int i=0;i<inList.size();i++){ TreeNode cur = inList.get(i); nums[levelMap.get(cur)-1][i] = cur.val; } // 打印二维数组 for(int i=0;i<row;i++){ for(int j=0;j<col;j++){ System.out.print(0 == nums[i][j] ? "\t": getPre0Str(nums[i][j])); } System.out.println(); } } // 获取中序遍历list public static List<TreeNode> getInList(TreeNode node){ List<TreeNode> result = new ArrayList<>(); Stack<TreeNode> stack = new Stack<>(); // 头节点入栈 stack.push(node); while(!stack.isEmpty()){ // 左子数入栈 while(node.left != null){ stack.push(node.left); node = node.left; } TreeNode cur = stack.pop(); result.add(cur); // 如果有右，则右节点入栈 if(null != cur.right){ stack.push(cur.right); // 将node指针指向右节点 node = cur.right; } } return result; } // 得到节点层级hash表和高度level public static int handleTreeLevel(Map<TreeNode,Integer> levelMap,TreeNode node){ int level = 1; Queue<TreeNode> queue = new LinkedList<>(); queue.offer(node); levelMap.put(node,level); while(!queue.isEmpty()){ TreeNode cur = queue.poll(); if(levelMap.get(cur) != level){ level++; } levelMap.put(cur,level); if(cur.left != null){ queue.offer(cur.left); levelMap.put(cur.left,level+1); } if(cur.right != null){ queue.offer(cur.right); levelMap.put(cur.right,level+1); } } return level; } // 获取4位补空格的字符串 public static String getPre0Str(int num){ String str = num+""; int count = 4 - str.length(); while (count>0){ str = " "+str; count--; } return str; } ~~~