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.
思路：太简单！
bool isSameTree(TreeNode *p, TreeNode *q) { if(p == NULL && q == NULL) return true; else if(p == NULL || q == NULL) return false; else if(p->val != q->val) return false; else { return isSameTree(p->left, q->left) && isSameTree(p->right, q->right); } }
原文：http://www.cnblogs.com/dplearning/p/4434875.html