Two problems : Same Tree and Symmetric Tree

1 . Given two binary trees, write a function to check if they are equal or not.
Two binary trees are considered equal if they are structurally identical and the nodes have the same value.

2.
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

Same tree

Symmetric tree

class Solution { public:     bool isSameTree(TreeNode *p, TreeNode *q) {         if (p==NULL && q==NULL) return true;         if ((p!=NULL && q==NULL)||(p==NULL&&q!=NULL))            return false;                 if (p->val==q->val)         {             return isSameTree(p->left,q->left)&isSameTree(p->right,q->right);         }         else             return false;             } };     Iterative solution class Solution { public:     bool isSameTree(TreeNode *p, TreeNode *q) {         stack<TreeNode *> st;         st.push(p);         st.push(q);                 while(!st.empty())         {             p = st.top();st.pop();             q = st.top(); st.pop();                         if (p==NULL&&q==NULL) continue;             if (p==NULL||q==NULL) return false;             if (p->val==q->val)             {                 st.push(p->left);                 st.push(q->left);                                 st.push(p->right);                 st.push(q->right);             }             else             return false;                     }                 return true;     } };

class Solution { public:     bool helper(TreeNode *left, TreeNode *right)     {         if (left==right && left==NULL)             return true;         if ((left==NULL&&right!=NULL)||(left!=NULL && right==NULL))             return false;         return ((left->val==right->val)&&helper(left->left,right->right)&&helper(left->right, right->left));     }        bool isSymmetric(TreeNode *root) {         return root?helper(root->left, root->right):true;     } };        Iterative solution class Solution { public:     bool isSymmetric(TreeNode *root) {         if (root==NULL||(root->left==NULL&&root->right==NULL))             return true;                 TreeNode *p = root->left, *q=root->right;                 stack<TreeNode*> st;         st.push(p);         st.push(q);                 while(!st.empty())         {             p =st.top(); st.pop();             q = st.top(); st.pop();                         if (p==NULL&&q==NULL) continue;             if (p==NULL||q==NULL) return false;                         if (p->val!=q->val) return false;                         st.push(p->left);             st.push(q->right);                         st.push(p->right);             st.push(q->left);         }                 return true;     } };