樹狀形式列印二叉樹

樹狀結構列印二叉樹，痛點在於確定節點之間的間隙。由於每個節點內容的長度不統一，在此處理方法是：選取每個最長的長度作為標準，其他的節點用空格符補齊。

對一個高為h的二叉樹，最底層（葉子節點），第一個節點距離起始輸出間隙為2^0 —1，節點之間的間隙為2^1—1。倒數第二層，第一個節點距離起始輸出間隙為2^1—1，節點之間的間隙為2^2—1。即，對於第k層（從上往下數，根節點為第一次），第一個節點距離起始輸出位置為2^（h-k）—1，節點之間的間隙為2^(h-k+1) —1。

在本例中，null**表示葉子節點的left、right節點。在插入節點時，輸入null**，在輸入節點內容，就可以完成插入操作。在代碼中，還額外實現了前、中、後序遍曆。

樹節點的代碼如下：

public class TreeNode {public String s;public TreeNode left;public TreeNode right;public TreeNode(){this.s = "null" + Tree.nullNum;Tree.nullNum++;left = null;right = null;}}

樹的代碼如下：

import java.util.ArrayList;import java.util.List;public class Tree {public static int nullNum = 0;private TreeNode root;public Tree(){initTree();}public void initTree(){nullNum = 0;root = new TreeNode();}public String printTree(){String tree = "";List<TreeNode> level = new ArrayList<TreeNode>();List<List<TreeNode>> wholeTree = new ArrayList<List<TreeNode>>();int maxLength = 0;level.add(root);while(level.size() > 0){wholeTree.add(level);List<TreeNode> newLevel = new ArrayList<TreeNode>();for (int i = 0; i < level.size(); i++){TreeNode node = level.get(i);if (node.s.length() > maxLength){maxLength = node.s.length();}if (node.left != null && node.right != null){newLevel.add(node.left);newLevel.add(node.right);}}level = newLevel;}int height = wholeTree.size();for (int i = 0; i < height; i++){level = wholeTree.get(i);int spaceNum = (int) ((Math.pow(2, height - i - 1) - 1) * (maxLength + 1));for (int j = 0; j < spaceNum; j++){tree += " ";}tree += addSpace(level.get(0).s,maxLength);spaceNum = (int) ((Math.pow(2, height - i) - 1) * (maxLength + 1));for (int j = 1; j < level.size(); j++){for (int k = 0; k < spaceNum; k++){tree += " ";}tree += addSpace(level.get(j).s,maxLength);}tree += "\n";}System.out.println(tree);return tree;}public String addSpace(String s, int length){int initLength = s.length();for(int i = 0; i < (length - initLength) / 2; i++){s = " " + s;} while(s.length() <= length){s += " ";}return s;}//插入節點public boolean insert(String position, String s){List<TreeNode> list = new ArrayList<TreeNode>();list.add(root);return insert(position,s,list);}public boolean insert(String position, String s, List<TreeNode> list){if(list.size() == 0){return false;}List<TreeNode> childList = new ArrayList<TreeNode>();for(int i = 0; i < list.size(); i++){TreeNode node = list.get(i);if (position.equals(node.s)){if (position.startsWith("null") && node.left == null && node.right == null){for (int j = 0; j < list.size(); j++){TreeNode temp = list.get(j);temp.left = new TreeNode();temp.right = new TreeNode();}}node.s = s;return true;}else{if (node.left != null){childList.add(node.left);}if (node.right != null){childList.add(node.right);}}}return insert(position,s,childList);}//前序走訪public String preOrder(){return preOrder(root);}public String preOrder(TreeNode pivot){String tree = "";if (! pivot.s.startsWith("null")){tree += pivot.s + " " + preOrder(pivot.left) + " " + preOrder(pivot.right) + " ";}return tree;}//中序遍曆public String inOrder(){return inOrder(root);}public String inOrder(TreeNode pivot){String tree = "";if (! pivot.s.startsWith("null")){tree += inOrder(pivot.left) + " " + pivot.s + " " + inOrder(pivot.right) + " ";}return tree;}//後序遍曆public String postOrder(){return postOrder(root);}public String postOrder(TreeNode pivot){String tree = "";if (! pivot.s.startsWith("null")){tree += postOrder(pivot.left) + " " + postOrder(pivot.right) + " " + pivot.s + " ";}return tree;}}

測試類別的代碼如下

mport java.util.Scanner;public class Test {public static void main(String[] args){Tree tree = new Tree();Scanner in = new Scanner(System.in);while(true){tree.printTree();System.out.println("請輸入需要插入的位置");String position = in.nextLine().trim().replace("\n", "");System.out.println("請輸入節點內容");String s = in.nextLine().trim().replace("\n", "");if(tree.insert(position, s) == false){System.out.println("你輸入的位置不存在...");break;}}}}

下面的是運行效果：