day-20 二叉树的层序遍历

思路：利用队列进行广度优先遍历即可

注意点：ArrayList执行remove之后，索引i会立即重排，注意可能越界

code:

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {

    public List<List<Integer>> levelOrder(TreeNode root) {


        List<List<Integer>> res=new ArrayList<List<Integer>>();
        if(root==null) return res;
        List<TreeNode> queue = new ArrayList<TreeNode>();
        queue.add(root);
        while(queue.size()>0){

            int size=queue.size();
           List<Integer> t = new ArrayList<Integer>();
            for(int i=0;i<size;i++){

                t.add(queue.get(i).val);
                if(queue.get(i).left!=null){

                    queue.add(queue.get(i).left);
                }
                if(queue.get(i).right!=null){

                    queue.add(queue.get(i).right);
                }  
            }
            for(int i=0;i<size;i++){

                queue.remove(0);
            }
            res.add(t);
        }
        return res;
    }
}

原文链接: https://blog.csdn.net/qq_53568730/article/details/136743074

目录