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:

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:

Given tree t:

   4
  / \
 1   2

Return false.

:::tip

serialize
hashset¶

:::

class Solution {
    public boolean isSubtree(TreeNode s, TreeNode t) {
        if (t == null) {
            return true;
        }
        if (s == null) {
            return false;
        }
        Set<String> hashset = new HashSet<>();
        String string_s = serialize(s, hashset, true);
        String string_t = serialize(t, hashset, false);
        return hashset.contains(string_t);
    }
    private String serialize(TreeNode s, Set<String> hashset, boolean save) {
        if (s == null) {
            return "";
        }
        String string = s.val + "," + serialize(s.left, hashset, save) + "," + serialize(s.right, hashset, save);
        if (save) {
            hashset.add(string);
        }
        return string;
    }
}

572 Subtree of Another Tree¶

hashset¶