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Title:
Please implement a function to print the binary tree in zigzag, that is, the first line is printed from left to right, the second layer is printed from right to left, the third line is printed from left to right, and so on.
Code idea:
Set two stacks, s2 for odd layer, s1 for even layer
When traversing s2 node, s1 is added in the order of left subtree and right subtree,
While traversing s1 node, s2 is added in the order of right subtree and left subtree.
Solution code:
import java.util.ArrayList;
import java.util.Stack;
/*
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> > res = new ArrayList<ArrayList<Integer> >();
Stack<TreeNode> s1 = new Stack<TreeNode>();
Stack<TreeNode> s2 = new Stack<TreeNode>();
int flag = 1;
if(pRoot == null)
return res;
s2.push(pRoot);
ArrayList<Integer> temp = new ArrayList<Integer>();
while(!s1.isEmpty() || !s2.isEmpty()){
if(flag % 2 != 0){
while(!s2.isEmpty()){
TreeNode node = s2.pop();
temp.add(node.val);
if(node.left != null){
s1.push(node.left);
}
if(node.right != null){
s1.push(node.right);
}
}
}
if(flag % 2 == 0){
while(!s1.isEmpty()){
TreeNode node = s1.pop();
temp.add(node.val);
if(node.right != null){
s2.push(node.right);
}
if(node.left != null){
s2.push(node.left);
}
}
}
res.add(new ArrayList<Integer>(temp));
temp.clear();
flag ++;
}
return res;
}
}
Reference article:
https://www.weiweiblog.cn/printz/