Real-world examples of recursion [closed]

Answer 1

Disabling/setting read-only for all children controls in a container control. I needed to do this because some of the children controls were containers themselves.

public static void SetReadOnly(Control ctrl, bool readOnly)
{
    //set the control read only
    SetControlReadOnly(ctrl, readOnly);

    if (ctrl.Controls != null && ctrl.Controls.Count > 0)
    {
        //recursively loop through all child controls
        foreach (Control c in ctrl.Controls)
            SetReadOnly(c, readOnly);
    }
}

Answer 2

Suppose you are building a CMS for a website, where your pages are in a tree structure, with say the root being the home-page.

Suppose also your {user|client|customer|boss} requests that you place a breadcrumb trail on every page to show where you are in the tree.

For any given page n, you'll may want to walk up to the parent of n, and its parent, and so on, recursively to build a list of nodes back up to the root of page tree.

Of course, you're hitting the db several times per page in that example, so you may want to use some SQL aliasing where you look up page-table as a, and page-table again as b, and join a.id with b.parent so you make the database do the recursive joins. It's been a while, so my syntax is probably not helpful.

Then again, you may just want to only calculate this once and store it with the page record, only updating it if you move the page. That'd probably be more efficient.

Anyway, that's my $.02

Answer 3

Quicksort, merge sort, and most other N-log N sorts.

Answer 4

Surely that many compilers out there use recursion heavily. Computer languages are inherently recursive themselves (i.e., you can embed 'if' statements inside other 'if' statements, etc.).

Answer 5

Parsing a tree of controls in Windows Forms or WebForms (.NET Windows Forms / ASP.NET).

Answer 6

Feedback loops in a hierarchical organization.

Top boss tells top executives to collect feedback from everyone in the company.

Each executive gathers his/her direct reports and tells them to gather feedback from their direct reports.

And on down the line.

People with no direct reports -- the leaf nodes in the tree -- give their feedback.

The feedback travels back up the tree with each manager adding his/her own feedback.

Eventually all the feedback makes it back up to the top boss.

This is the natural solution because the recursive method allows filtering at each level -- the collating of duplicates and the removal of offensive feedback. The top boss could send a global email and have each employee report feedback directly back to him/her, but there are the "you can't handle the truth" and the "you're fired" problems, so recursion works best here.