Package org.jgrapht.alg.util
Class UnionFind<T>
- java.lang.Object
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- org.jgrapht.alg.util.UnionFind<T>
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- Type Parameters:
T
- element type
public class UnionFind<T> extends java.lang.Object
An implementation of Union Find data structure. Union Find is a disjoint-set data structure. It supports two operations: finding the set a specific element is in, and merging two sets. The implementation uses union by rank and path compression to achieve an amortized cost of $O(\alpha(n))$ per operation where $\alpha$ is the inverse Ackermann function. UnionFind uses the hashCode and equals method of the elements it operates on.- Author:
- Tom Conerly
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description void
addElement(T element)
Adds a new element to the data structure in its own set.T
find(T element)
Returns the representative element of the set that element is in.protected java.util.Map<T,T>
getParentMap()
protected java.util.Map<T,java.lang.Integer>
getRankMap()
boolean
inSameSet(T element1, T element2)
Tests whether two elements are contained in the same set.int
numberOfSets()
Returns the number of sets.void
reset()
Resets the UnionFind data structure: each element is placed in its own singleton set.int
size()
Returns the total number of elements in this data structure.java.lang.String
toString()
Returns a string representation of this data structure.void
union(T element1, T element2)
Merges the sets which contain element1 and element2.
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Constructor Detail
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UnionFind
public UnionFind(java.util.Set<T> elements)
Creates a UnionFind instance with all the elements in separate sets.- Parameters:
elements
- the initial elements to include (each element in a singleton set).
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Method Detail
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addElement
public void addElement(T element)
Adds a new element to the data structure in its own set.- Parameters:
element
- The element to add.
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getParentMap
protected java.util.Map<T,T> getParentMap()
- Returns:
- map from element to parent element
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getRankMap
protected java.util.Map<T,java.lang.Integer> getRankMap()
- Returns:
- map from element to rank
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find
public T find(T element)
Returns the representative element of the set that element is in.- Parameters:
element
- The element to find.- Returns:
- The element representing the set the element is in.
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union
public void union(T element1, T element2)
Merges the sets which contain element1 and element2. No guarantees are given as to which element becomes the representative of the resulting (merged) set: this can be either find(element1) or find(element2).- Parameters:
element1
- The first element to union.element2
- The second element to union.
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inSameSet
public boolean inSameSet(T element1, T element2)
Tests whether two elements are contained in the same set.- Parameters:
element1
- first elementelement2
- second element- Returns:
- true if element1 and element2 are contained in the same set, false otherwise.
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numberOfSets
public int numberOfSets()
Returns the number of sets. Initially, all items are in their own set. The smallest number of sets equals one.- Returns:
- the number of sets
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size
public int size()
Returns the total number of elements in this data structure.- Returns:
- the total number of elements in this data structure.
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reset
public void reset()
Resets the UnionFind data structure: each element is placed in its own singleton set.
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toString
public java.lang.String toString()
Returns a string representation of this data structure. Each component is represented as $\left{v_i:v_1,v_2,v_3,...v_n\right}$, where $v_i$ is the representative of the set.- Overrides:
toString
in classjava.lang.Object
- Returns:
- string representation of this data structure
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