题目描述
给定一颗二叉树,分别实现按层和 ZigZag 打印二叉树。
ZigZag遍历: 意思是第一层从左到右遍历,第二层从右到左遍历,依次类推。
输入描述:
第一行输入两个整数 n 和 root,n 表示二叉树的总节点个数,root 表示二叉树的根节点。
以下 n 行每行三个整数 fa,lch,rch,表示 fa 的左儿子为 lch,右儿子为 rch。(如果 lch 为 0 则表示 fa 没有左儿子,rch同理)
输出描述:
先输出按层打印,再输出按ZigZag打印。
示例1
输入
8 1
1 2 3
2 4 0
4 0 0
3 5 6
5 7 8
7 0 0
8 0 0
6 0 0
输出
Level 1 : 1
Level 2 : 2 3
Level 3 : 4 5 6
Level 4 : 7 8
Level 1 from left to right: 1
Level 2 from right to left: 3 2
Level 3 from left to right: 4 5 6
Level 4 from right to left: 8 7
解法一:利用队列和双栈
import java.io.*;
import java.util.*;
public class Main{
public static void main(String[] args) throws Exception{
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
br.readLine();
TreeNode root = createTree(br);
layerPrint(root);
zigZag(root);
}
public static void zigZag(TreeNode root){
if(root==null) return;
Stack<TreeNode> s1 = new Stack<>();
Stack<TreeNode> s2 = new Stack<>();
s1.add(root);
int level = 1;
TreeNode node;
StringBuilder sb;
while(!s1.isEmpty()||!s2.isEmpty()){
if(!s1.isEmpty()){
sb = new StringBuilder();
sb.append("Level "+level+" from left to right: ");
while(!s1.isEmpty()){
node = s1.pop();
sb.append(node.val+" ");
if(node.left!=null){
s2.add(node.left);
}
if(node.right!=null){
s2.add(node.right);
}
}
level++;
System.out.println(sb.toString().trim());
}
if(!s2.isEmpty()){
sb = new StringBuilder();
sb.append("Level "+level+" from right to left: ");
while(!s2.isEmpty()){
node = s2.pop();
sb.append(node.val+" ");
if(node.right!=null){
s1.add(node.right);
}
if(node.left!=null){
s1.add(node.left);
}
}
level++;
System.out.println(sb.toString().trim());
}
}
}
public static void layerPrint(TreeNode root){
if(root==null) return;
Queue<TreeNode> q = new LinkedList<>();
q.add(root);
int presize = 1;
int size = 0;
int count = 1;
while(!q.isEmpty()){
StringBuilder sb = new StringBuilder();
sb.append("Level "+count+" : ");
while((presize--)>0){
TreeNode node = q.poll();
sb.append(node.val+" ");
if(node.left!=null){
size++;
q.add(node.left);
}
if(node.right!=null){
size++;
q.add(node.right);
}
}
presize = size;
size = 0;
count++;
System.out.println(sb.toString().trim());
}
}
//递归建树
public static TreeNode createTree(BufferedReader br){
try{
String[] ss = br.readLine().trim().split(" ");
int data = Integer.parseInt(ss[0]);
int left = Integer.parseInt(ss[1]);
int right = Integer.parseInt(ss[2]);
TreeNode root = new TreeNode(data);
if(left!=0){
root.left = createTree(br);
}
if(right!=0){
root.right = createTree(br);
}
return root;
}catch(Exception e){
return null;
}
}
}
class TreeNode{
int val;
TreeNode left;
TreeNode right;
public TreeNode(int val){
this.val = val;
}
}