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graph.js
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graph.js
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class Graph {
constructor() {
this.adjacency_matrix = [];
this.node_ids = [];
this.nodes = [];
this.indexes = [];
}
addNode(id, priority) {
this.adjacency_matrix.push(Array(this.getNoOfNodes()).fill(0));
for (const row of this.adjacency_matrix) {
row.push(0);
}
this.node_ids.push(id);
this.nodes.push({ id, priority });
this.indexes.push(this.nodes.length - 1);
}
getNoOfNodes() {
return this.nodes.length;
}
addEdge(id_i, id_j) {
const [i, j] = this._getIndexesOfNodePair(id_i, id_j);
this.adjacency_matrix[i][j] = 1;
}
_getIndexesOfNodePair(id_i, id_j) {
return [this.node_ids.indexOf(id_i), this.node_ids.indexOf(id_j)];
}
pathExists(id_i, id_j) {
const [i, j] = this._getIndexesOfNodePair(id_i, id_j);
return this._pathExists(i, j);
}
_pathExists(i, j) {
if (this.adjacency_matrix[i][j]) {
return true;
}
for (let k = 0; k < this.getNoOfNodes(); ++k) {
if (this.adjacency_matrix[i][k]) {
return this._pathExists(k, j);
}
}
return false;
}
bestFirstSearch() {
this.front = [];
this.visited = [];
while (this.visited.length < this.nodes.length) {
const { front_node, next_node } = this._getNextNode();
this.visited.push(next_node);
if (front_node !== null) {
if (this._areAllSuccessorsVisited(front_node)) {
const index = this.front.indexOf(front_node);
this.front.splice(index, 1);
}
}
if (!this._areAllSuccessorsVisited(next_node)) {
this.front.push(next_node);
}
}
return this.visited.map(i => this.nodes[i].id);
}
_areAllSuccessorsVisited(i) {
for (let j = 0; j < this.nodes.length; ++j) {
if (this.adjacency_matrix[i][j] && !this._isVisited(j)) {
return false;
}
}
return true;
}
_isVisited(i) {
return this.visited.includes(i);
}
_isNodeWithoutPredecessors(i) {
for (let j = 0; j < this.nodes.length; ++j) {
if (this.adjacency_matrix[j][i]) {
return false;
}
}
return true;
}
_getNextNode() {
const nodesWithoutPredecessorsYetToBeVisited = this.indexes.filter(
i => this._isNodeWithoutPredecessors(i) && !this._isVisited(i)
);
const candidate1 = this._lookForNextNodeInCandidates(
nodesWithoutPredecessorsYetToBeVisited
);
if (candidate1.priority === Graph.MAX_PRIORITY) {
return { front_node: null, next_node: candidate1.index };
}
const successorsYetToBeVisited = this.front.reduce((successors, i) => {
this.indexes
.filter(j => this.adjacency_matrix[i][j] && !this._isVisited(j))
.map(j => successors.add(j));
return successors;
}, new Set());
const candidate2 = this._lookForNextNodeInCandidates(
successorsYetToBeVisited
);
if (candidate1.priority < candidate2.priority) {
return { front_node: null, next_node: candidate1.index };
}
if (candidate1.priority === candidate2.priority) {
if (
candidate1.mean_priority_of_succcessors <
candidate2.mean_priority_of_succcessors
) {
return { front_node: null, next_node: candidate1.index };
}
}
const front_node = this.indexes.find(
i => this.adjacency_matrix[i][candidate2.index]
);
return { front_node, next_node: candidate2.index };
}
_lookForNextNodeInCandidates(candidates) {
let next_node = null,
best_priority = Infinity,
current_mean,
best_mean = Infinity;
for (const candidate of candidates) {
if (this.nodes[candidate].priority < best_priority) {
best_priority = this.nodes[candidate].priority;
best_mean = this._meanPriorityOfSuccessors(candidate);
next_node = candidate;
if (this.nodes[candidate].priority === Graph.MAX_PRIORITY) {
break;
}
} else if (this.nodes[candidate].priority === best_priority) {
current_mean = this._meanPriorityOfSuccessors(candidate);
if (current_mean < best_mean) {
best_mean = current_mean;
next_node = candidate;
}
}
}
return {
index: next_node,
priority: best_priority,
mean_priority_of_succcessors: best_mean,
};
}
_meanPriorityOfSuccessors(i) {
let sum = 0,
length = 0;
for (let j of this.indexes) {
if (this.adjacency_matrix[i][j] && !this._isVisited(j)) {
sum += this.nodes[j].priority;
++length;
}
}
return length > 0 ? sum / length : 0;
}
}
Graph.MAX_PRIORITY = 0;
module.exports = Graph;

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