Leetcode oj:symmetric tree tree (symmetrical trees)

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  3

But the following are not:

    1   /   2   2   \      3    3

Judging whether a tree is symmetrical, the first method of recursion is of course easier to solve:

1 /**2 * Definition for a binary tree node.3 * struct TreeNode {4 * int val;5 * TreeNode *left;6 * TreeNode *right;7 * TreeNode (int x): Val (x), left (null), right (null) {}8  * };9  */Ten classSolution { One  Public: A     BOOLIssymmetric (treenode*root) { -         if(Root = =NULL) -             return true; the         if(!root->left &&!root->Right ) -             return true; -         if(Root->left &&!root->right | |!root->left && root->Right ) -             return false; +         returnChecksymmetric (Root->left, root->Right ); -     } +  A     BOOLChecksymmetric (TreeNode * left, TreeNode *Right ) at     { -         if(!left &&!)Right ) -             return true; -         if(!left && Right | | Left &&!Right ) -             return false; -         if(Left->val! = right->val) in             return false; -         returnChecksymmetric (Left->left, Right->right) && checksymmetric (Left->right, right->Left ); to     } +};

The topic is also required to be implemented in a non-recursive manner, creating two queues that can be implemented:

1 /**2 * Definition for a binary tree node.3 * struct TreeNode {4 * int val;5 * TreeNode *left;6 * TreeNode *right;7 * TreeNode (int x): Val (x), left (null), right (null) {}8  * };9  */Ten classSolution { One  Public: A     BOOLIssymmetric (treenode*root) { -Queue<treenode *>Q1; -Queue<treenode *>Q2; the         if(Root = NULL)return true; -         if(!root->left &&!root->right)return true; -         if(Root->left &&!root->right | |!root->left && root->right)return false;//Val -Q1.push (root->Left ); +Q2.push (root->Right ); -TreeNode * Tmpleft, *Tmpright; +          while(!q1.empty () &&!Q2.empty ()) { ATmpleft =Q1.front (); atTmpright =Q2.front (); - Q1.pop (), Q2.pop (); -             if(!tmpleft &&!)tmpright) -                 Continue; -             if(!tmpleft && tmpright | | tmpleft &&!tmpright) -                 return false; in             if(Tmpleft->val! = tmpright->val) -                 return false; toQ1.push (tmpleft->Left ); +Q1.push (tmpleft->Right ); -Q2.push (tmpright->Right ); theQ2.push (tmpright->Left ); *         } $         returnQ1.empty () &&q2.empty ();Panax Notoginseng     } -};

Leetcode oj:symmetric tree tree (symmetrical trees)