Symmetric Tree

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

For example, this binary tree is symmetric:

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

But the following is not:

    1   / \  2   2   \   \   3    3

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

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

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    bool isSymmetric(TreeNode *root) {        vector<int> arr(0);        queue<TreeNode*> q;        vector<int>::iterator index_begin,index_end;        TreeNode *leaf;        int cnt=1,i;        int leaves=0;                TreeNode *p = root;        if(p==NULL) return true;        q.push(p);        while(!q.empty()){            arr.clear();            for(i=0,leaves=0;i<cnt;i++){                p=q.front();                arr.push_back(p->val);                q.pop();                if(p->val==-999) continue;                if(p->left!=NULL) {                    q.push(p->left);                    leaves++;                }                else {                    leaf=(TreeNode*)malloc(sizeof(TreeNode));                    leaf->val=-999;                    q.push(leaf);                    leaves++;                }                               if(p->right!=NULL) {                    q.push(p->right);                    leaves++;                }                else {                    leaf=(TreeNode*)malloc(sizeof(TreeNode));                    leaf->val=-999;                    q.push(leaf);                    leaves++;                }            }            cnt=leaves;            if(cnt%2!=0) return false;            index_begin=arr.begin();            index_end=arr.end()-1;            while(index_begin<index_end){                if(*index_begin!=*index_end) return false;                index_begin++;                index_end--;            }                    }        return true;    }};