面试准备之--二叉树的递归与非递归方式

来源：互联网发布：治痘痘最好的方法知乎编辑：程序博客网时间：2024/05/18 18:42

思路请参考：http://www.nowcoder.com/courses/1/7/1

三种二叉树递归方式：

import java.util.*; /*public class TreeNode {    int val = 0;    TreeNode left = null;    TreeNode right = null;    public TreeNode(int val) {        this.val = val;    }}*/public class TreeToSequence {    public int[][] convert(TreeNode root) {        // write code here        List<TreeNode> preList = new LinkedList<>();//定义List        List<TreeNode> inList = new LinkedList<>();        List<TreeNode> afterList = new LinkedList<>();        preOrder(root,preList);//先序遍历函数        inOrder(root,inList);//中序遍历函数        afterOrder(root,afterList);//后序遍历函数        int size = preList.size();        int[][] ans = new int[3][];//返回的二维数组        int[] pre = new int[size];        int[] in = new int[size];        int[] after = new int[size];        for(int i = 0;i < size;++ i){            pre[i] = preList.get(i).val;            in[i] = inList.get(i).val;            after[i] = afterList.get(i).val;        }        ans[0] = pre;        ans[1] = in;        ans[2] = after;        return ans;    }    public void preOrder(TreeNode root,List<TreeNode> preList){        if(root == null)            return;        preList.add(root);        preOrder(root.left,preList);        preOrder(root.right,preList);    }    public void inOrder(TreeNode root,List<TreeNode> inList){        if(root == null)            return;        inOrder(root.left,inList);        inList.add(root);        inOrder(root.right,inList);    }    public void afterOrder(TreeNode root,List<TreeNode> afterList){        if(root == null)            return;        afterOrder(root.left,afterList);        afterOrder(root.right,afterList);        afterList.add(root);    }}

二叉树的非递归方式

import java.util.*; /*public class TreeNode {    int val = 0;    TreeNode left = null;    TreeNode right = null;    public TreeNode(int val) {        this.val = val;    }}*/public class TreeToSequence {    public int[][] convert(TreeNode root) {        // write code here        LinkedList<Integer> left=new  LinkedList<Integer>();        LinkedList<Integer> mid=new  LinkedList<Integer>();        LinkedList<Integer> right=new  LinkedList<Integer>();        firstPrint(root,left);        midPrint(root,mid);        afterPrint(root,right);        int[][] res=new int[3][left.size()];        for(int i=0;i<left.size();i++){            res[0][i]=left.get(i);            res[1][i]=mid.get(i);            res[2][i]=right.get(i);        }        return res;             }    public void midPrint(TreeNode root,LinkedList<Integer> res){        if(root==null)            return ;        midPrint(root.left,res);        res.add(root.val);        midPrint(root.right,res);             }             public void firstPrint(TreeNode root,LinkedList<Integer> res){        if(root==null)            return ;        res.add(root.val);        firstPrint(root.left,res);          firstPrint(root.right,res);             }             public void afterPrint(TreeNode root,LinkedList<Integer> res){        if(root==null)            return ;        afterPrint(root.left,res);        afterPrint(root.right,res);        res.add(root.val);                      }}

0 0