Building nested TreeNode array in Typescript

Question

Given a flat one dimensional array of type TreeNode (see interface definition below), I would like to traverse the array and add subsequent array elements as children.

Would be great to do recursively, my shot at non-recursion uses a buffer, but the issue I am facing is how to do node.children[0].children[0]...children[0] as notice that there is only one child per parent.

    Childify(results: TreeNode[]): any {
    var node: TreeNode;
    var buffer: TreeNode;
    var count: number = 0;

    for (var res of results) {
        if (count == 0) {
            node = res[0];
            buffer = res[0];
            buffer.children = [];
            node.children = [];
        } else if (count == 1) {
            buffer.children = res[0];
        } else {
            node = buffer;
            node.children = [];
            node.children.push(res[0]);
            buffer = <TreeNode>node.children;
        }

        count++;
    }
}

Interface definition:

export interface TreeNode {
label?: string;
data?: any;
icon?: any;
expandedIcon?: any;
collapsedIcon?: any;
children?: TreeNode[];  <---------------
leaf?: boolean;
expanded?: boolean;
type?: string;
parent?: TreeNode;
partialSelected?: boolean;
styleClass?: string;
draggable?: boolean;
droppable?: boolean;
selectable?: boolean;

}

The input:

TreeNode[] = [treeNode1, treeNode2, treeNode3, treeNode4,...,treeNodeX]

The output is a TreeNode object, nested by the children property (which is also of TreeNode type):

TreeNode = treeNode1
treeNode1.children = treeNode2
treeNode2.children = treeNode3
treeNode3.children = treeNode4
treeNodeX-1.children = treeNodeX

I don't know how to envoke treeNode1.children[0].children[0]......children[0] dynamically for X number of children in a loop, to assign to the next level of children in treeNode1.

Based on what are you inserting the nodes? How do you want the resulting three to look like? — Lazar Ljubenović
– Lazar Ljubenović, Commented Feb 12, 2019 at 16:54

Aadit M Shah · Accepted Answer · 2019-02-18 05:09:44Z

2

+50

I don't know TypeScript but here's how I'd do this in JavaScript:

const input = [ new TreeNode("node1")
              , new TreeNode("node2")
              , new TreeNode("node3")
              , new TreeNode("node4")
              , new TreeNode("node5")
              ];

const output = input.reduceRight((child, parent) => {
    parent.children.push(child);
    return parent;
});

console.log(output);

function TreeNode(name) {
    this.name = name;
    this.children = [];
}

Hope that helps.

answered Feb 18, 2019 at 5:09

Aadit M Shah

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Comments

Norman Breau · Accepted Answer · 2019-02-16 03:19:06Z

I've built an algorithm for you. I've built it in simple javascript, but it should be easily modifiable to conform to your typescript interface.

And the code is here:

var flatNodes = [
    {
        name: 'node1',
        children: []
    },
    {
        name: 'node2',
        children: []
    },
    {
        name: 'node3',
        children: []
    },
    {
        name: 'node4',
        children: []
    },
    {
        name: 'node5',
        children: []
    }
];

function linkNodes(flatNodes) {
    flatNodes = flatNodes.slice(); //copy the list

    flatNodes = flatNodes.reverse();

    for (var i = 1; i < flatNodes.length; i++) {
        var previousNode = flatNodes[i - 1];
        var currentNode = flatNodes[i];

        currentNode.children.push(previousNode);
    }

    return flatNodes[flatNodes.length - 1];
}

console.log(linkNodes(flatNodes));

The output is here:

{
    "name": "node1",
    "children": [
        {
            "name": "node2",
            "children": [
                {
                    "name": "node3",
                    "children": [
                        {
                            "name": "node4",
                            "children": [
                                {
                                    "name": "node5",
                                    "children": []
                                }
                            ]
                        }
                    ]
                }
            ]
        }
    ]
}

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