572. Subtree of Another Tree.md

572. Subtree of Another Tree

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Difficulty : Easy

Related Topics : Tree

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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.

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Solution

• mine
  • Java
    • Runtime: 5 ms, faster than 97.29%, Memory Usage: 39.4 MB, less than 6.39% of Java online submissions

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

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