Breadth First Search Example

Utils

enum Colors {
  WHITE = 0,
  GREY = 1,
  BLACK = 2,
}

const initializeColor = (vertices: (string | number)[]) => {
  const color: any = {};
  for (let i = 0; i < vertices.length; i++) {
    color[vertices[i]] = Colors.WHITE;
  }
  return color;
};

No Weights

function breadthFirstSearch(graph: Graph, callback: Function) {
  const vertices = graph.getVertices();
  const adjList = graph.getAdjList();
  const color = initializeColor(vertices);
  const queue = new Queue();
  queue.enqueue(vertices);

  while (!queue.isEmpty()) {
    const u = queue.dequeue();
    const neighbors = adjList.get(u);
    color[u] = Colors.GREY;
    for (let i = 0; i < neighbors.length; i++) {
      const w = neighbors[i];
      if (color[w] === Colors.WHITE) {
        color[w] = Colors.GREY;
        queue.enqueue(w);
      }
    }
    color[u] = Colors.BLACK;
    if (callback) {
      callback(u);
    }
  }
}

With weights

function breadthFirstSearch(graph: Graph, startVertex: number) {
  const vertices = graph.getVertices();
  const adjList = graph.getAdjList();
  const color = initializeColor(vertices);
  const queue = new Queue();
  const distances: any = {};
  const predecessors: any = {};
  queue.enqueue(startVertex);

  for (let i = 0; i < vertices.length; i++) {
    distances[vertices[i]] = 0;
    predecessors[vertices[i]] = null;
  }

  while (!queue.isEmpty()) {
    const u = queue.dequeue(),
      neighbors = adjList.get(u);
    color[u] = Colors.GREY;
    for (let i = 0; i < neighbors.length; i++) {
      const w = neighbors[i];
      if (color[w] === Colors.WHITE) {
        color[w] = Colors.GREY;
        distances[w] = distances[u] + 1;
        predecessors[w] = u;
        queue.enqueue(w);
      }
    }
    color[u] = Colors.BLACK;
  }

  return {
    distances: distances,
    predecessors: predecessors,
  };
}