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.

题目解析：

判断两个树是否相同，就一个结点信息一个结点信息判断。如果一个为空一个不为空或者结点值不相等，都返回FALSE。

递归判断子树即可。

/**
 * 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 isSameTree(TreeNode *p, TreeNode *q) {
        if(p == NULL && q == NULL)
            return true;
        if(p != NULL && q == NULL)
            return false;
        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);
    }
};