/*
* Disjoint-set data structure - Library (TypeScript)
*
* Copyright (c) 2021 Project Nayuki. (MIT License)
* https://www.nayuki.io/page/disjoint-set-data-structure
*
* Permission is hereby granted, free of charge, to any person obtaining a copy of
* this software and associated documentation files (the "Software"), to deal in
* the Software without restriction, including without limitation the rights to
* use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
* the Software, and to permit persons to whom the Software is furnished to do so,
* subject to the following conditions:
* - The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
* - The Software is provided "as is", without warranty of any kind, express or
* implied, including but not limited to the warranties of merchantability,
* fitness for a particular purpose and noninfringement. In no event shall the
* authors or copyright holders be liable for any claim, damages or other
* liability, whether in an action of contract, tort or otherwise, arising from,
* out of or in connection with the Software or the use or other dealings in the
* Software.
*/
/*
* Represents a set of disjoint sets. Also known as the union-find data structure.
* Main operations are querying if two elements are in the same set, and merging two sets together.
* Useful for testing graph connectivity, and is used in Kruskal's algorithm.
*/
class DisjointSet {
// Global properties
private numSets: number = 0;
// Per-node property arrays. This representation is more space-efficient than creating one node object per element.
private parents: Array = []; // The index of the parent element. An element is a representative iff its parent is itself.
private sizes : Array = []; // Positive number if the element is a representative, otherwise zero.
// Constructs a new set containing the given number of singleton sets.
// For example, new DisjointSet(3) --> {{0}, {1}, {2}}.
public constructor(numElems: number) {
if (numElems < 0)
throw "Number of elements must be non-negative";
for (let i = 0; i < numElems; i++)
this.addSet();
}
// Returns the number of elements among the set of disjoint sets. All the other methods
// require the argument elemIndex to satisfy 0 <= elemIndex < getNumElements().
public getNumElements(): number {
return this.parents.length;
}
// Returns the number of disjoint sets overall. 0 <= result <= getNumElements().
public getNumSets(): number {
return this.numSets;
}
// Returns the representative element for the set containing the given element. This method is also
// known as "find" in the literature. Also performs path compression, which alters the internal state to
// improve the speed of future queries, but has no externally visible effect on the values returned.
private getRepr(elemIndex: number): number {
if (elemIndex < 0 || elemIndex >= this.parents.length)
throw "Element index out of bounds";
// Follow parent pointers until we reach a representative
let parent: number = this.parents[elemIndex];
while (true) {
const grandparent: number = this.parents[parent];
if (grandparent == parent)
return parent;
this.parents[elemIndex] = grandparent; // Partial path compression
elemIndex = parent;
parent = grandparent;
}
}
// Returns the size of the set that the given element is a member of. 1 <= result <= getNumElements().
public getSizeOfSet(elemIndex: number): number {
return this.sizes[this.getRepr(elemIndex)];
}
// Tests whether the given two elements are members of the same set. Note that the arguments are orderless.
public areInSameSet(elemIndex0: number, elemIndex1: number): boolean {
return this.getRepr(elemIndex0) == this.getRepr(elemIndex1);
}
// Adds a new singleton set, incrementing getNumElements() and getNumSets().
// Returns the identity of the new element, which equals the old value of getNumElements().
public addSet(): number {
const elemIndex: number = this.getNumElements();
this.parents.push(elemIndex);
this.sizes.push(1);
this.numSets++;
return elemIndex;
}
// Merges together the sets that the given two elements belong to. This method is also known as "union" in the literature.
// If the two elements belong to different sets, then the two sets are merged and the method returns true.
// Otherwise they belong in the same set, nothing is changed and the method returns false. Note that the arguments are orderless.
public mergeSets(elemIndex0: number, elemIndex1: number): boolean {
// Get representatives
let repr0: number = this.getRepr(elemIndex0);
let repr1: number = this.getRepr(elemIndex1);
if (repr0 == repr1)
return false;
// Compare sizes to choose parent node
if (this.sizes[repr0] < this.sizes[repr1]) {
let temp: number = repr0;
repr0 = repr1;
repr1 = temp;
}
// Now repr0's size >= repr1's size
// Graft repr1's subtree onto node repr0
this.parents[repr1] = repr0;
this.sizes[repr0] += this.sizes[repr1];
this.sizes[repr1] = 0;
this.numSets--;
return true;
}
// For unit tests. This detects many but not all invalid data structures, throwing an exception
// if a structural invariant is known to be violated. This always returns silently on a valid object.
public checkStructure(): void {
let numRepr: number = 0;
let sizeSum: number = 0;
for (let i = 0; i < this.parents.length; i++) {
const parent: number = this.parents[i];
const size : number = this.sizes [i];
const isRepr: boolean = parent == i;
if (isRepr)
numRepr++;
let ok: boolean = true;
ok = ok && 0 <= parent && parent < this.parents.length;
ok = ok && (!isRepr && size == 0 || isRepr && 1 <= size && size <= this.parents.length);
if (!ok)
throw "Assertion error";
sizeSum += size;
}
if (!(0 <= this.numSets && this.numSets == numRepr && this.numSets <= this.parents.length && this.parents.length == sizeSum))
throw "Assertion error";
}
}