Given two binary trees, write a function to check if they are the same or not.

Two binary trees are considered the same if they are structurally identical and the nodes have the same value.

Example 1:

Input:     1         1
          / \       / \
         2   3     2   3

        [1,2,3],   [1,2,3]

Output: true

Example 2:

Input:     1         1
          /           \
         2             2

        [1,2],     [1,null,2]

Output: false

Example 3:

Input:     1         1
          / \       / \
         2   1     1   2

        [1,2,1],   [1,1,2]

Output: false

时间复杂度O（n）

class Solution {
    public:
 bool isSameTree(TreeNode *p, TreeNode *q) {
 if (!p && !q) return true;
 if (!p || !q) return false;
 return p->val == q->val;
 && isSameTree(p->left, q->left)
 && isSameTree(p->right, q->right);
    }
};