剑指Offer（书）：树的子结构

public boolean HasSubtree(TreeNode root1, TreeNode root2) {
    boolean result = false;
    if (root1 != null && root2 != null) {
        if (root1.val == root2.val) {
            result = DoesTreeHaveTree(root1, root2);
        }
        if (!result) {
            result = HasSubtree(root1.left, root2);
        }
        if (!result) {
            result = HasSubtree(root1.right, root2);
        }
    }
    return result;
}

private boolean DoesTreeHaveTree(TreeNode root1, TreeNode root2) {
    if (root2 == null) {
        return true;
    }
    if (root1 == null) {
        return false;
    }
    if (root1.val != root2.val) {
        return false;
    }
    return DoesTreeHaveTree(root1.left, root2.left) && DoesTreeHaveTree(root1.right, root2.right);
}