其实就是横着打印,一排一排的。通过队列实现。
模版
public void LevelOrder() { Queue<Node> queue = new Queue<Node>(); queue.Enqueue(_head); while (queue.Count>0)//队列中还有结点 { Node node = (Node)queue.Dequeue(); Console.Write(node);//打印结点 if (node.Left != null) { queue.Enqueue(node.Left); } if (node.Right!=null) { queue.Enqueue(node.Right); } } }
之字形打印二叉树
public class Solution { public ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) { Queue<TreeNode> queue=new LinkedList<TreeNode>(); boolean reverse = false; ArrayList<ArrayList<Integer>> ret = new ArrayList<>(); queue.add(pRoot); while(!queue.isEmpty()){ ArrayList<Integer> list = new ArrayList<>(); int c = queue.size(); while(c-- > 0){ TreeNode node = queue.poll(); if(node == null){ continue;//空节点不加到list里面 } list.add(node.val); queue.add(node.left); queue.add(node.right); } if(reverse){ Collections.reverse(list); } reverse = !reverse; if(list.size() != 0){ ret.add(list); } } return ret; } }
二叉树的右视图
解析:打印每一行的最后一个
/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ class Solution { public List<Integer> rightSideView(TreeNode root) { if(root==null){ return new ArrayList<>(); } ArrayList<Integer> res = new ArrayList<>(); Queue<TreeNode> queue = new LinkedList<>(); queue.add(root); while(!queue.isEmpty()){ int len= queue.size(); for(int i=0;i<len;i++){ TreeNode node = queue.poll(); if(i==len-1){ res.add(node.val); } if(node.left != null){ queue.add(node.left); } if(node.right != null){ queue.add(node.right); } } } return res; }}