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）

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/**
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) {
        boolean result = false;

        if(root1 != null && root2 != null)
        {
            if(root1.val == root2.val)
                result = DoesTree1HaveTree2(root1,root2);
            if(!result)
                result = HasSubtree(root1.left,root2);
            if(!result)
                result = HasSubtree(root1.right,root2);
        }
        return result;
    }

    public boolean DoesTree1HaveTree2(TreeNode root1, TreeNode root2)
    {
        if(root2 == null)
            return true;
        if(root1 == null)
            return false;

        if(root1.val != root2.val)
            return false;

        return DoesTree1HaveTree2(root1.left,root2.left) && DoesTree1HaveTree2(root1.right,root2.right);
    }
}