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let elesfn = ({
// kruskal's algorithm (finds min spanning tree, assuming undirected graph)
// implemented from pseudocode from wikipedia
kruskal: function( weightFn ){
weightFn = weightFn || ( edge => 1 );
let { nodes, edges } = this.byGroup();
let numNodes = nodes.length;
let forest = new Array(numNodes);
let A = nodes; // assumes byGroup() creates new collections that can be safely mutated
let findSetIndex = ele => {
for( let i = 0; i < forest.length; i++ ){
let eles = forest[i];
if( eles.has(ele) ){ return i; }
}
};
// start with one forest per node
for( let i = 0; i < numNodes; i++ ){
forest[i] = this.spawn( nodes[i] );
}
let S = edges.sort( (a, b) => weightFn(a) - weightFn(b) );
for( let i = 0; i < S.length; i++ ){
let edge = S[i];
let u = edge.source()[0];
let v = edge.target()[0];
let setUIndex = findSetIndex(u);
let setVIndex = findSetIndex(v);
let setU = forest[ setUIndex ];
let setV = forest[ setVIndex ];
if( setUIndex !== setVIndex ){
A.merge( edge );
// combine forests for u and v
setU.merge( setV );
forest.splice( setVIndex, 1 );
}
}
return A;
}
});
export default elesfn;
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