NC14 按之字形顺序打印二叉树
描述
给定一个二叉树,返回该二叉树的之字形层序遍历,(第一层从左向右,下一层从右向左,一直这样交替)
例如:
给定的二叉树是{1,2,3,#,#,4,5}
该二叉树之字形层序遍历的结果是
[
[1],
[3,2],
[4,5]
]
示例2
输入:
{8,6,10,5,7,9,11}
复制
返回值:
[[8],[10,6],[5,7,9,11]]
import java.util.*;
/*
public class TreeNode {
int val = 0;
TreeNode left = null;
TreeNode right = null;
public TreeNode(int val) {
this.val = val;
}
}
*/
public class Solution {
public ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
ArrayList<ArrayList<Integer>> ans = new ArrayList<>();
if(pRoot == null){
return ans ;
}
Stack<TreeNode> stack1 = new Stack<TreeNode>() ;
Stack<TreeNode> stack2 = new Stack<TreeNode>() ;
int layer = 1 ;
stack1.push(pRoot);
while(!stack1.isEmpty() || !stack2.isEmpty()){
if(layer % 2 != 0){
ArrayList<Integer> level = new ArrayList<>() ;
int size = stack1.size() ;
for(int i = 0 ; i < size ; i++){
TreeNode node = stack1.pop() ;
level.add(node.val) ;
if(node.left != null){
stack2.push(node.left);
}
if(node.right != null){
stack2.push(node.right) ;
}
}
ans.add(level) ;
layer++ ;
}else{
ArrayList<Integer> level = new ArrayList<>() ;
int size = stack2.size() ;
for(int i = 0 ; i < size ; i++){
TreeNode node = stack2.pop() ;
level.add(node.val) ;
if(node.right != null){
stack1.push(node.right) ;
}
if(node.left != null){
stack1.push(node.left);
}
}
ans.add(level) ;
layer++ ;
}
}
return ans ;
}
}