題目描述

分別按照二叉樹先序，中序和后序打印所有的節點。

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輸入

{1,2,3}

返回值

[[1,2,3],[2,1,3],[2,3,1]]

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import java.util.ArrayList;class TreeNode {int val;TreeNode left;TreeNode right;TreeNode(int x) { val = x; } }public class ThreeOrdersTree {public static void main(String[] args) {}/**** @param root TreeNode類 the root of binary tree* @return int整型二維數組*/public int[][] threeOrders (TreeNode root) {if(null == root){return null;}ArrayList<Integer> arrayList = new ArrayList<>();firstShow(root,arrayList);int[][] arrAll = new int[3][arrayList.size()];for (int i = 0; i < arrayList.size(); i++) {arrAll[0][i] = arrayList.get(i);}arrayList.clear();middleShow(root,arrayList);for (int i = 0; i < arrayList.size(); i++) {arrAll[1][i] = arrayList.get(i);}arrayList.clear();postShow(root,arrayList);for (int i = 0; i < arrayList.size(); i++) {arrAll[2][i] = arrayList.get(i);}return arrAll;}// 前序遍歷private void firstShow(TreeNode root,ArrayList<Integer> arrayList){if(null == root){return;}arrayList.add(root.val);if(null != root.left){firstShow(root.left, arrayList);}if(null != root.right){firstShow(root.right,arrayList);}}// 中序遍歷private void middleShow(TreeNode root,ArrayList<Integer> arrayList){if(null == root){return;}if(null != root.left){middleShow(root.left, arrayList);}arrayList.add(root.val);if(null != root.right){middleShow(root.right,arrayList);}}// 后序遍歷private void postShow(TreeNode root,ArrayList<Integer> arrayList){if(null == root){return;}if(null != root.left){postShow(root.left, arrayList);}if(null != root.right){postShow(root.right,arrayList);}arrayList.add(root.val);} }

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