572. Subtree of Another Tree

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(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，尝试每一个s的subtree和t是不是same tree，如果是就返回true，否则等耗尽了所有s的node还没碰到相同的，就返回false