100. Same Tree

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.

用递归的深度优先算法
类似先序遍历，先判断p->val是否等于q->val，然后在遍历p的左子树是否等于q的左子树，以及p的右子树是否等于q的右子树

class Solution {public:    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);    }};