572. Subtree of Another Tree

Question

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.

Solution:

  • Method 1: Recursion ```Java /**
    • Definition for a binary tree node.
    • public class TreeNode {
    • int val;
    • TreeNode left;
    • TreeNode right;
    • TreeNode(int x) { val = x; }
    • } */ class Solution { public boolean isSubtree(TreeNode s, TreeNode t) { if(s != null && t != null) return same(s, t) || (isSubtree(s.left, t) || isSubtree(s.right, t)); else if(s != null || t != null) return false; else return true; } private boolean same(TreeNode s, TreeNode t){ if(s != null && t != null) return s.val == t.val && same(s.left, t.left) && same(s.right, t.right); else if(s != null || t != null) return false; else return true; } } ```

Second Time

  • Method 1: Recursion ```Java /**
    • Definition for a binary tree node.
    • public class TreeNode {
    • int val;
    • TreeNode left;
    • TreeNode right;
    • TreeNode(int x) { val = x; }
    • } */ class Solution { public boolean isSubtree(TreeNode s, TreeNode t) { if(s != null && t != null){ return isSame(s, t) || isSubtree(s.left, t) || isSubtree(s.right, t); }else if(s == null && t == null) return true; return false; } private boolean isSame(TreeNode s, TreeNode t){ if(s != null && t != null){ if(s.val != t.val) return false; return isSame(s.left, t.left) && isSame(s.right, t.right); }else if(s == null && t == null) return true; return false; } } ```