Leetcode---101. Symmetric Tree

Title Link: Symmetric Tree

Given a binary tree, check whether it is a mirror of the itself (ie, symmetric around its center).

For example, this binary tree is symmetric:

    1    / \   2   2  / \ / \ 3  4 4  

But the following are not:

    1    / \   2   2    \   \    3    

Note:

Bonus points if you could solve it both recursively and iteratively.

Confused what "{1,#,2,3}" means? > read more about how binary tree was serialized on OJ.

OJ ' s Binary Tree serialization:

The serialization of a binary tree follows a level order traversal, where ' # ' signifies a path terminator where no node ex Ists below.

Here's an example:

   1   / \  2   3     /    4     \      

The above binary tree is serialized as "{1,2,3,#,#,4,#,#,5}".

The requirement of this question is to judge whether a tree is symmetrical.

The idea of recursion, similar to the same Tree, is only here to judge symmetry.

The two subtrees trees L and R symmetric, that is, the nodes of L and R are the same, and the right subtree of Zuozi and R is symmetric and the right subtree of L and the left subtree of R are symmetric.

Time complexity: O (N)

Space complexity: O (1)

1 class Solution2 {3  Public:4     BOOL Issymmetric(TreeNode *Root)5     {6         if(Root == NULL)7             return true;8         return Issymmetric(Root  -  Left, Root  -  Right);9     }Ten Private: One     BOOL Issymmetric(TreeNode *L, TreeNode *R) A     { -         if(L != NULL && R != NULL) -             return L  - Val == R  - Val  the                 && Issymmetric(L  -  Left, R  -  Right)  -                 && Issymmetric(L  -  Right, R  -  Left); -         Else -             return L == NULL && R == NULL; +     } - };

As for the method of iteration, not to be continued ...

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Leetcode---101. Symmetric Tree