leetcode-572-easy

Subtree of Another Tree

Given the roots of two binary trees root and subRoot, return true if there is a subtree of root with the same structure and node values of subRoot and false otherwise.

A subtree of a binary tree tree is a tree that consists of a node in tree and all of this node's descendants. The tree tree could also be considered as a subtree of itself.

Example 1:

Input: root = [3,4,5,1,2], subRoot = [4,1,2]
Output: true
Example 2:

Input: root = [3,4,5,1,2,null,null,null,null,0], subRoot = [4,1,2]
Output: false
Constraints:

The number of nodes in the root tree is in the range [1, 2000].
The number of nodes in the subRoot tree is in the range [1, 1000].
-104 <= root.val <= 104
-104 <= subRoot.val <= 104

思路一：检测 root 的每个节点值，如果和 subRoot 根节点相同，检测从此节点开始的子树是否和 subRoot 相等

    public boolean isSubtree(TreeNode root, TreeNode subRoot) {
        if (root == null || subRoot == null) {
            return false;
        }

        if (root.val == subRoot.val) {
            if (checkSubtree(root, subRoot)) {
                return true;
            }
        }

        return isSubtree(root.left, subRoot) || isSubtree(root.right, subRoot);
    }

    public boolean checkSubtree(TreeNode root, TreeNode subRoot) {
        if (root == null && subRoot == null) {
            return true;
        } else if (root != null && subRoot != null && root.val == subRoot.val) {
            return checkSubtree(root.left, subRoot.left) && checkSubtree(root.right, subRoot.right);
        } else {
            return false;
        }
    }