Why Graphs Exist and What Trees Cannot Model in DSA Typescript - Test Your Knowledge

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a graph node with a list of neighbors.

DSA Typescript

class GraphNode {
  value: number;
  neighbors: GraphNode[];
  constructor(value: number) {
    this.value = value;
    this.neighbors = [1];
  }
}

Drag options to blanks, or click blank then click option'

A[]

B{}

Cnull

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using {} which creates an object instead of an array.

Setting neighbors to null or 0 which are not lists.

The neighbors list should be initialized as an empty array to hold connected nodes.

2fill in blank

medium

Complete the code to add an edge between two graph nodes.

DSA Typescript

function addEdge(node1: GraphNode, node2: GraphNode) {
  node1.neighbors.[1](node2);
  node2.neighbors.push(node1);
}

Drag options to blanks, or click blank then click option'

Aappend

Binsert

Cadd

Dpush

Attempts:

3 left

💡 Hint

Common Mistakes

Using append which is not a method on arrays in TypeScript.

Using add or insert which are not valid array methods.

The push method adds an element to the end of an array in TypeScript.

3fill in blank

hard

Fix the error in the code to check if a graph has a cycle.

DSA Typescript

function hasCycle(node: GraphNode, visited: Set<number>): boolean {
  if (visited.has(node.value)) {
    return [1];
  }
  visited.add(node.value);
  for (const neighbor of node.neighbors) {
    if (hasCycle(neighbor, visited)) {
      return true;
    }
  }
  return false;
}

Drag options to blanks, or click blank then click option'

Afalse

Btrue

Cnull

Dundefined

Attempts:

3 left

💡 Hint

Common Mistakes

Returning false which means no cycle found incorrectly.

Returning null or undefined which are not boolean values.

If the node was already visited, it means a cycle exists, so return true.

4fill in blank

hard

Fill both blanks to create an adjacency list representation of a graph.

DSA Typescript

const graph: [1] = {};
function addEdge(u: number, v: number) {
  if (!graph[u]) graph[u] = [2];
  graph[u].push(v);
}

Drag options to blanks, or click blank then click option'

ARecord<number, number[]>

BArray<number>

C[]

D{}

Attempts:

3 left

💡 Hint

Common Mistakes

Using {} for adjacency lists which is an object, not an array.

Using Array as the graph type which is incorrect.

The graph is a record mapping numbers to arrays of numbers. Initialize empty arrays for adjacency lists.

5fill in blank

hard

Fill all three blanks to implement a breadth-first search (BFS) on a graph.

DSA Typescript

function bfs(start: number, graph: Record<number, number[]>): number[] {
  const visited = new Set<number>();
  const queue: number[] = [start];
  const result: number[] = [];
  while (queue.length > 0) {
    const node = queue.[1]();
    if (!visited.has(node)) {
      visited.add(node);
      result.push(node);
      for (const neighbor of graph[node] || []) {
        if (!visited.has(neighbor)) {
          queue.[2](neighbor);
        }
      }
    }
  }
  return [3];
}

Drag options to blanks, or click blank then click option'

Ashift

Bpush

Cresult

Dpop

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop() which removes from the end, causing DFS behavior.

Returning queue instead of the result list.

Use shift() to dequeue from the front, push() to enqueue neighbors, and return the result list.