Leetcode 107 : 二叉树的层次遍历2

偏执的太偏执、 2022-10-16 07:13 108阅读 0赞

https://leetcode-cn.com/problems/binary-tree-inorder-traversal/

考察点： 二叉树的层次遍历， 集合类的灵活应用 Collections 以及 list.add(0,)方法的灵活使用

import BasicDataStruct.TreeNode; 
    
        import java.util.*;
    
        public class LeetCode107FLoorTraversal {
        
    
            public static List<List<Integer>> inorderTraversal(TreeNode root) {
        
    
                List<List<Integer>> list = new ArrayList<>();
                Queue<TreeNode> queue = new LinkedList<>();
                queue.offer(root);
                while (!queue.isEmpty()) {
        
                    int size = queue.size();
                    List<Integer> subList = new ArrayList<>();
                    for (int i = 0; i < size; i++) {
        
                        TreeNode node = queue.poll();
                        subList.add(node.getVal());
                        if (node.left != null) {
        
                            queue.add(node.left);
                        }
                        if (node.right != null) {
        
                            queue.add(node.right);
                        }
                    }
                    // 也可以list.add(0,subList);
                    list.add(subList);
                }
                Collections.reverse(list);
                
                return list;
            }
    
    
            public static void main(String[] args) {
        
                TreeNode root = new TreeNode(1);
                root.left = new TreeNode(2);
                root.right = new TreeNode(3);
                root.left.left = new TreeNode(4);
                root.left.right = new TreeNode(5);
                root.right.left = new TreeNode(6);
                root.right.right = new TreeNode(7);
                System.out.println(inorderTraversal(root).toString());
            }
    
        }