leecode 101. 对称二叉树

水深无声 2022-10-15 09:57 200阅读 0赞

### 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  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODMzNjY1OA_size_16_color_FFFFFF_t_70]

# 官网题解 #

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODMzNjY1OA_size_16_color_FFFFFF_t_70 1]

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);
        }
    }

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODMzNjY1OA_size_16_color_FFFFFF_t_70]: /images/20221014/802e596d744e40808b0cdf3693647822.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zODMzNjY1OA_size_16_color_FFFFFF_t_70 1]: /images/20221014/18198550e66f43fdb76b4507f3bb93c2.png