How to Generate a Hierarchical HTML Tree from Parent-Child Relationships?

Hierarchical Tree Generation from Parent-Child Relationships

Challenge:

Convert a collection of name-parentname pairs into a hierarchical tree structure. The goal is to generate nested HTML unordered lists (

) representing the child-parent relationships.

Recursive Approach:

The solution employs two recursive functions. The first function, parseTree(), traverses the tree structure and constructs a hierarchical tree. It searches for direct children of a specified root and adds them to the resulting tree, recursively parsing each child's children.

function parseTree($tree, $root = null) {
    $return = array();
    foreach($tree as $child => $parent) {
        if($parent == $root) {
            unset($tree[$child]);
            $return[] = array(
                'name' => $child,
                'children' => parseTree($tree, $child)
            );
        }
    }
    return empty($return) ? null : $return;    
}

The second function, printTree(), traverses the tree generated by parseTree() and prints the corresponding HTML unordered list.

function printTree($tree) {
    if(!is_null($tree) && count($tree) > 0) {
        echo '<ul>';
        foreach($tree as $node) {
            echo '<li>'.$node['name'];
            printTree($node['children']);
            echo '</li>';
        }
        echo '</ul>';
    }
}

Usage:

To convert the given name-parentname pairs into a tree structure and print the HTML unordered list, you would call these functions as follows:

$result = parseTree($tree);
printTree($result);

Combined Function:

For improved efficiency, you can merge the two functions into a single function:

function parseAndPrintTree($root, $tree) {
    $return = array();
    if(!is_null($tree) && count($tree) > 0) {
        echo '<ul>';
        foreach($tree as $child => $parent) {
            if($parent == $root) {                    
                unset($tree[$child]);
                echo '<li>'.$child;
                parseAndPrintTree($child, $tree);
                echo '</li>';
            }
        }
        echo '</ul>';
    }
}

This combined function simplifies the parsing and printing process and reduces the number of iterations required.

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