treeBFSelect.js

// Implement a breadth-first method on a tree class.
// BFSelect accepts a filter function, calls that function on each of the nodes in Breadth-First order,
// and returns a flat array of node values of the tree for which the filter returns true.

var Tree = function(value){
  this.value = value;
  this.children = [];
};

Tree.prototype.BFSelect = function(filter, oldQ, depth, results) {
  var queue = oldQ || new Queue();
  var depth = depth || 0;
  var results = results || [];
  
  for (var i = 0; i < this.children.length; i++) {
    queue.push([this.children[i], depth+1]);
  }
  
  if(filter(this.value, depth)) {
    results.push(this.value);
  }
  
  var next = queue.pop();
  if(next) {
    next[0].BFSelect(filter,queue,next[1],results);
  }
  
  return results;
};

var Queue = function() {
  var storage = [];

  this.push = function(item) {
    storage.push(item);
  };

  this.pop = function() {
    return storage.shift();
  };
};

/**
  * add an immediate child
  * (wrap values in Tree nodes if they're not already)
  */
Tree.prototype.addChild = function(child){
  if (!child || !(child instanceof Tree)){
    child = new Tree(child);
  }

  if(!this.isDescendant(child)){
    this.children.push(child);
  }else {
    throw new Error('That child is already a child of this tree');
  }
  // return the new child node for convenience
  return child;
};

/**
  * check to see if the provided tree is already a child of this
  * tree __or any of its sub trees__
  */
Tree.prototype.isDescendant = function(child){
  if(this.children.indexOf(child) !== -1){
    // `child` is an immediate child of this tree
    return true;
  }else{
    for(var i = 0; i < this.children.length; i++){
      if(this.children[i].isDescendant(child)){
        // `child` is descendant of this tree
        return true;
      }
    }
    return false;
  }
};

/**
  * remove an immediate child
  */
Tree.prototype.removeChild = function(child){
  var index = this.children.indexOf(child);
  if(index !== -1){
    // remove the child
    this.children.splice(index,1);
  }else{
    throw new Error('That node is not an immediate child of this tree');
  }
};