leecode 101. 对称二叉树

Posted 2021-06-09 go大鸡腿

文章目录

• 题目
• 题解
• 代码
• 官网题解

题目

给定一个二叉树，检查它是否是镜像对称的。

题解

我这个方法还是广度遍历，然后储存起来在进行对比

代码

class Solution {

public static class TreeNodes extends TreeNode{
        int level;
        TreeNodes(TreeNode node,int level){
            this.level = level;
            this.val = node.val;
            this.left = node.left;
            this.right = node.right;
        }
    }

    public static boolean isSymmetric(TreeNode root) {
       Queue<TreeNodes> queue = new LinkedList<>();
        queue.add(new TreeNodes(root,1));
        int level = 1;
        List<TreeNode> list =new ArrayList<>();
        while (!queue.isEmpty()) {
            TreeNodes node = queue.poll();
            if(node.level != level){
                level++;
                if(!check(list)){
                    return false;
                }
                list =new ArrayList<>();
            }
            if (node.left != null) {
                queue.add(new TreeNodes(node.left, node.level+1));
                list.add(node.left);
            }else{
                node.left = new TreeNode(-1); 
                list.add(node.left);
            }
            if (node.right != null) {
                queue.add(new TreeNodes(node.right,node.level+1));
                list.add(node.right);
            }else{
                node.right= new TreeNode(-1);  
                list.add(node.right);
            }
            
        }
        return true;
    }

    public static boolean check(List<TreeNode> list){
        int i = list.size()/2-1;
        int j = list.size()/2;
        while(i>=0&&j<=list.size()-1){
            int a = list.get(i).val;
            int b = list.get(j).val;
            if(a!=b){
                return false;
            }
            i--;j++;
        }
        return true;
    }
}

但是

结果很一般

官网题解

class Solution {
    public boolean isSymmetric(TreeNode root) {
        return check(root, root);
    }

    public boolean check(TreeNode p, TreeNode q) {
        if (p == null && q == null) {
            return true;
        }
        if (p == null || q == null) {
            return false;
        }
        return p.val == q.val && check(p.left, q.right) && check(p.right, q.left);
    }
}