求二叉树的层序遍历

Posted 2021-07-07 编程实战与原理

给定一个二叉树，返回该二叉树层序遍历的结果，（从左到右，一层一层地遍历）
例如：
给定的二叉树是{3,9,20,#,#,15,7},

输出

[

[3],
[9,20],
[15,7]
]

输入：

{1,2,3,4,#,#,5}

复制

返回值：

[[1],[2,3],[4,5]]

代码实现如下：

import java.util.ArrayList;import java.util.LinkedList;import java.util.Queue;
public class Test {
 public static void main(String[] args) { TreeNode t1 = new TreeNode(1); t1.left = new TreeNode(2); t1.right = new TreeNode(3); t1.right.left = new TreeNode(4); t1.right.right = new TreeNode(5); System.out.println(levelNum(t1)); }
 public static ArrayList<ArrayList<Integer>> levelNum(TreeNode node) { ArrayList<ArrayList<Integer>> arrayLists = new ArrayList<>(); if (null == node) { return arrayLists; } //用于存储每一层的节点 Queue<TreeNode> queue = new LinkedList<>(); queue.add(node); while (!queue.isEmpty()) { //用于存储当前遍历这一层的节点 ArrayList<Integer> arrayList = new ArrayList<>(); int n = queue.size(); for (int i = 0; i < n; i++) { TreeNode tn = queue.poll(); arrayList.add(tn.val); if (null != tn.left) { queue.add(tn.left); } if (null != tn.right) { queue.add(tn.right); }
 }
 arrayLists.add(arrayList); }
 return arrayLists; }
 /** * 定义树 */ public static class TreeNode { private int val; private TreeNode left; private TreeNode right;
 public TreeNode(int val) { this.val = val; }
 public int getVal() { return val; }
 public void setVal(int val) { this.val = val; }
 public TreeNode getLeft() { return left; }
 public void setLeft(TreeNode left) { this.left = left; }
 public TreeNode getRight() { return right; }
 public void setRight(TreeNode right) { this.right = right; } }
}