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Title:
The binary tree is printed from top to bottom, and the nodes of the same layer are output from left to right. Output one line per layer.
Code idea:
Sequence traversal of binary tree is realized by queue. We need two variables: a start to record the number of nodes that have been printed in the current layer, an end to record the number of all nodes in the layer before, and a start == end to start the next layer after traversing the current layer in the table.
Solution code:
import java.util.ArrayList;
import java.util.Queue;
import java.util.LinkedList;
/*
public class TreeNode {
int val = 0;
TreeNode left = null;
TreeNode right = null;
public TreeNode(int val) {
this.val = val;
}
}
*/
public class Solution {
ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
ArrayList<ArrayList<Integer> > res = new ArrayList<ArrayList<Integer> >();
if(pRoot == null)
return res;
ArrayList<Integer> temp = new ArrayList<Integer>();
Queue<TreeNode> layer = new LinkedList<TreeNode>();
layer.offer(pRoot);
int start = 0, end = 1;
while(!layer.isEmpty()){
TreeNode node = layer.poll();
temp.add(node.val);
start ++;
if(node.left != null)
layer.add(node.left);
if(node.right != null)
layer.add(node.right);
if(start == end){
start = 0;
res.add(temp);
temp = new ArrayList<Integer>();
end = layer.size();
}
}
return res;
}
}
Reference article:
https://www.weiweiblog.cn/print/