26、树的子结构

输入两棵二叉树A，B，判断B是不是A的子结构。（ps：我们约定空树不是任意一个树的子结构）

题目链接：https://www.nowcoder.com/practice/6e196c44c7004d15b1610b9afca8bd88

/**
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }
}
*/
public class Solution {
    
    public boolean HasSubtree(TreeNode root1, TreeNode root2) {
        if (root1 == null || root2 == null) return false;

        boolean result = isSubtree(root1, root2);
        if (!result) result = HasSubtree(root1.left, root2);
        if (!result) result = HasSubtree(root1.right, root2);

        return result;
    }

    private boolean isSubtree(TreeNode root1, TreeNode root2) {
        if (root2 == null) return true;
        if (root1 == null) return false;

        if (root1.val != root2.val) return false;
        return isSubtree(root1.left, root2.left) && isSubtree(root1.right, root2.right);
    }
}