L572. Subtree of Another Tree

Problem:

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.

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