problem：
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.
Tree Depth-first Searchthinking：
使用深搜，一边检查结构一边检查数值
code：
class Solution {
public:
bool isSameTree(TreeNode *p, TreeNode *q) {
if(p==NULL && q==NULL)
return true;
if(p==NULL||q==NULL)
return false;
if(p->val!=q->val)
return false;
return isSameTree(p->left,q->left)&&isSameTree(p->right,q->right);
}
};原文：http://blog.csdn.net/hustyangju/article/details/45099577