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Java/DataStructures/Graphs/Graphs.java at master · codesica/Java · GitHub
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import
java
.
util
.
ArrayList
;
import
java
.
lang
.
StringBuilder
;
class
AdjacencyListGraph
<
E
extends
Comparable
<
E
>> {
ArrayList
<
Vertex
>
verticies
;
public
AdjacencyListGraph
() {
verticies
=
new
ArrayList
<>();
}
private
class
Vertex
{
E
data
;
ArrayList
<
Vertex
>
adjacentVerticies
;
public
Vertex
(
E
data
) {
adjacentVerticies
=
new
ArrayList
<>();
this
.
data
=
data
;
}
public
boolean
addAdjacentVertex
(
Vertex
to
) {
for
(
Vertex
v
:
adjacentVerticies
) {
if
(
v
.
data
.
compareTo
(
to
.
data
) ==
0
) {
return
false
;
// the edge already exists
}
}
return
adjacentVerticies
.
add
(
to
);
// this will return true;
}
public
boolean
removeAdjacentVertex
(
E
to
) {
// use indexes here so it is possible to
// remove easily without implementing
// equals method that ArrayList.remove(Object o) uses
for
(
int
i
=
0
;
i
<
adjacentVerticies
.
size
();
i
++) {
if
(
adjacentVerticies
.
get
(
i
).
data
.
compareTo
(
to
) ==
0
) {
adjacentVerticies
.
remove
(
i
);
return
true
;
}
}
return
false
;
}
}
/**
* this method removes an edge from the graph between two specified
* verticies
*
* @param from the data of the vertex the edge is from
* @param to the data of the vertex the edge is going to
* @return returns false if the edge doesn't exist, returns true if the edge exists and is removed
*/
public
boolean
removeEdge
(
E
from
,
E
to
) {
Vertex
fromV
=
null
;
for
(
Vertex
v
:
verticies
) {
if
(
from
.
compareTo
(
v
.
data
) ==
0
) {
fromV
=
v
;
break
;
}
}
if
(
fromV
==
null
)
return
false
;
return
fromV
.
removeAdjacentVertex
(
to
);
}
/**
* this method adds an edge to the graph between two specified
* verticies
*
* @param from the data of the vertex the edge is from
* @param to the data of the vertex the edge is going to
* @return returns true if the edge did not exist, return false if it already did
*/
public
boolean
addEdge
(
E
from
,
E
to
) {
Vertex
fromV
=
null
,
toV
=
null
;
for
(
Vertex
v
:
verticies
) {
if
(
from
.
compareTo
(
v
.
data
) ==
0
) {
// see if from vertex already exists
fromV
=
v
;
}
else
if
(
to
.
compareTo
(
v
.
data
) ==
0
) {
// see if to vertex already exists
toV
=
v
;
}
if
(
fromV
!=
null
&&
toV
!=
null
)
break
;
// both nodes exist so stop searching
}
if
(
fromV
==
null
) {
fromV
=
new
Vertex
(
from
);
verticies
.
add
(
fromV
);
}
if
(
toV
==
null
) {
toV
=
new
Vertex
(
to
);
verticies
.
add
(
toV
);
}
return
fromV
.
addAdjacentVertex
(
toV
);
}
/**
* this gives a list of verticies in the graph and their adjacencies
*
* @return returns a string describing this graph
*/
public
String
toString
() {
StringBuilder
sb
=
new
StringBuilder
();
for
(
Vertex
v
:
verticies
) {
sb
.
append
(
"Vertex: "
);
sb
.
append
(
v
.
data
);
sb
.
append
(
"
\n
"
);
sb
.
append
(
"Adjacent verticies: "
);
for
(
Vertex
v2
:
v
.
adjacentVerticies
) {
sb
.
append
(
v2
.
data
);
sb
.
append
(
" "
);
}
sb
.
append
(
"
\n
"
);
}
return
sb
.
toString
();
}
}
public
class
Graphs
{
public
static
void
main
(
String
args
[]) {
AdjacencyListGraph
<
Integer
>
graph
=
new
AdjacencyListGraph
<>();
assert
graph
.
addEdge
(
1
,
2
);
assert
graph
.
addEdge
(
1
,
5
);
assert
graph
.
addEdge
(
2
,
5
);
assert
!
graph
.
addEdge
(
1
,
2
);
assert
graph
.
addEdge
(
2
,
3
);
assert
graph
.
addEdge
(
3
,
4
);
assert
graph
.
addEdge
(
4
,
1
);
assert
!
graph
.
addEdge
(
2
,
3
);
System
.
out
.
println
(
graph
);
}
}
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