Given twonon-emptybinary treessandt, check whether treethas exactly the same structure and node values with a subtree ofs. A subtree ofsis a tree consists of a node insand all of this node's descendants. The treescould also be considered as a subtree of itself.

Example 1:
Given tree s:

     3
    / \
   4   5
  / \
 1   2

Given tree t:

   4 
  / \
 1   2

Returntrue, 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

Returnfalse.

class Solution {
    public boolean isSubtree(TreeNode s, TreeNode t) {
        
 
if(s == null) return false;
        if(isSametree(s, t)) return true;
        return isSubtree(s.left, t) || isSubtree(s.right, t);
    }
    public boolean isSametree(TreeNode t1, TreeNode t2) {
        if(t1 == null && t2 == null) return true;
        if(t1 == null || t2 == null) return false
 
;
        if(t1.val != t2.val) return false;
        return isSametree(t1.left, t2.left) && isSametree(t1.right, t2.right);
    }
}

和issametree差不多，嘗試每一個s的subtree和t是不是same tree，如果是就返回true，否則等耗盡了所有s的node還沒碰到相同的，就返回false