LeetCode572 另一棵树的子树

Given two non-empty binary trees s and t, check whether tree t has exactly the same structure and node values with a subtree of s. A subtree of s is a tree consists of a node in s and all of this node’s descendants. The tree s could also be considered as a subtree of itself.

Example 1:
Given tree s:

 3
/ \

4 5
/
1 2
Given tree t:
4
/
1 2
Return true, because t has the same structure and node values with a subtree of s.
Example 2:
Given tree s:

 3
/ \

4 5
/
1 2
/
0
Given tree t:
4
/
1 2
Return false.

class Solution {
    public boolean isSubtree(TreeNode s, TreeNode t) {
        if(s == null) return false;
        if(isSame(s, t)) return true;
        return isSubtree(s.left, t) || isSubtree(s.right, t);
    }
    public boolean isSame(TreeNode s, TreeNode t){
        if(s == null || t == null) return s == t;
        if(s.val != t.val) return false;
        return isSame(s.left,t.left) && isSame(s.right,t.right);
    }
}