Another tree subtree

Given two binary nonempty s and t, and the test is included in s t subtrees having the same structure and the node values. s of a subtree including all the descendants of a node and the node s. s can be seen as its own subtree.

Example 1:
given tree s:

 3
/ \

4 5
/
1 2

Given a tree t:

4
/
1 2

Returns true, because t to s a subtree and nodes have the same configuration values.

Example 2:
given tree s:

 3
/ \

4 5
/
1 2
/
0

Given a tree t:

4
/
1 2

Return false.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public boolean 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);
    }
    public boolean isSubtree(TreeNode s, TreeNode t) {
        if(s==null){
            return false;
        }
        if(t==null){
            return true;
        }
        if(s.val==t.val&&isSameTree(s,t)){
            return true;
        }
        return isSubtree(s.left,t)||isSubtree(s.right,t);
    }
}