Skip to content

Commit 8500ffa

Browse files
phishman3579phishman3579
committed
Merge branch 'push-relabel' of https://github.com/wodomierz/java-algorithms-implementation into wodomierz-push-relabel
2 parents 5981258 + 97c279b commit 8500ffa

File tree

2 files changed

+293
-0
lines changed

2 files changed

+293
-0
lines changed

‎src/com/jwetherell/algorithms/graph/PushRelabel.java‎

Lines changed: 240 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,240 @@
1+
package com.jwetherell.algorithms.graph;
2+
3+
import com.jwetherell.algorithms.data_structures.Graph;
4+
5+
import java.util.ArrayList;
6+
import java.util.Collection;
7+
import java.util.LinkedList;
8+
import java.util.Map;
9+
import java.util.Queue;
10+
import java.util.TreeMap;
11+
12+
/**
13+
* @author mrowka
14+
*/
15+
public class PushRelabel {
16+
17+
private static class Vertex {
18+
boolean visited = false;
19+
int h;
20+
int currentEdge;
21+
long excess;
22+
ArrayList<Edge> edges = new ArrayList<Edge>();
23+
}
24+
25+
private static class Edge {
26+
long c;
27+
long f;
28+
Vertex from;
29+
Vertex to;
30+
Edge revertedEdge;
31+
32+
Edge(Vertex from, Vertex to, long c) {
33+
this.from = from;
34+
this.to = to;
35+
this.c = c;
36+
37+
}
38+
39+
Edge(Vertex from, Vertex to) {
40+
this.from = from;
41+
this.to = to;
42+
}
43+
44+
@Override
45+
public boolean equals(Object o) {
46+
if (this == o) {
47+
return true;
48+
}
49+
50+
if (o == null || getClass() != o.getClass()) {
51+
return false;
52+
}
53+
54+
Edge edge = (Edge) o;
55+
56+
if (!from.equals(edge.from)) {
57+
return false;
58+
}
59+
return to.equals(edge.to);
60+
61+
}
62+
63+
@Override
64+
public int hashCode() {
65+
int result = from.hashCode();
66+
result = 31 * result + to.hashCode();
67+
return result;
68+
}
69+
}
70+
71+
private Queue<Vertex> q = new LinkedList<Vertex>();
72+
private int relabelCounter;
73+
private int n;
74+
private ArrayList<Vertex> vertices = new ArrayList<Vertex>();
75+
76+
private Vertex s;
77+
private Vertex t;
78+
79+
private PushRelabel(Collection<Vertex> vertices, Vertex s, Vertex t) {
80+
this.vertices.addAll(vertices);
81+
this.s = s;
82+
this.t = t;
83+
this.n = vertices.size();
84+
}
85+
86+
/**
87+
* Computes maximum flow in flow network, using push-relabel algorithm with O(V^3) complexity.
88+
*
89+
* @param edgesToCapacities represents edges of network with capacities
90+
* @param source source of network
91+
* @param sink sink of network
92+
* @param <T> parameter of graph on which network is based
93+
* @return the maximum flow
94+
*/
95+
public static <T extends Comparable<T>> Long getMaximumFlow(Map<Graph.Edge<T>, Long> edgesToCapacities, Graph.Vertex<T> source, Graph.Vertex<T> sink) {
96+
if (edgesToCapacities == null) {
97+
throw new IllegalArgumentException("Graph is NULL.");
98+
}
99+
100+
Map<Graph.Vertex<T>, Vertex> vertexMap = new TreeMap<Graph.Vertex<T>, Vertex>();
101+
102+
103+
for (Graph.Edge<T> edge : edgesToCapacities.keySet()) {
104+
vertexMap.put(edge.getFromVertex(), new Vertex());
105+
vertexMap.put(edge.getToVertex(), new Vertex());
106+
}
107+
Vertex s = new Vertex();
108+
Vertex t = new Vertex();
109+
vertexMap.put(source, s);
110+
vertexMap.put(sink, t);
111+
112+
113+
PushRelabel pushRelabel = new PushRelabel(vertexMap.values(), s, t);
114+
115+
for (Map.Entry<Graph.Edge<T>, Long> edgeWithCapacity : edgesToCapacities.entrySet()) {
116+
pushRelabel.addEdge(
117+
vertexMap.get(edgeWithCapacity.getKey().getFromVertex()),
118+
vertexMap.get(edgeWithCapacity.getKey().getToVertex()),
119+
edgeWithCapacity.getValue()
120+
);
121+
}
122+
123+
return pushRelabel.maxFlow();
124+
}
125+
126+
private void addEdge(Vertex from, Vertex to, long c) {
127+
int placeOfEdge = from.edges.indexOf(new Edge(from, to));
128+
if (placeOfEdge == -1) {
129+
Edge edge = new Edge(from, to, c);
130+
Edge revertedEdge = new Edge(to, from, 0);
131+
edge.revertedEdge = revertedEdge;
132+
revertedEdge.revertedEdge = edge;
133+
from.edges.add(edge);
134+
to.edges.add(revertedEdge);
135+
} else {
136+
from.edges.get(placeOfEdge).c += c;
137+
}
138+
}
139+
140+
private void recomputeHeigh() {
141+
Queue<Vertex> que = new LinkedList<Vertex>();
142+
for (Vertex vertex : vertices) {
143+
vertex.visited = false;
144+
vertex.h = 2 * n;
145+
}
146+
147+
t.h = 0;
148+
s.h = n;
149+
s.visited = true;
150+
t.visited = true;
151+
que.add(t);
152+
while (!que.isEmpty()) {
153+
Vertex act = que.poll();
154+
for (Edge e : act.edges) {
155+
if (!e.to.visited && e.revertedEdge.c > e.revertedEdge.f) {
156+
e.to.h = act.h + 1;
157+
que.add(e.to);
158+
e.to.visited = true;
159+
}
160+
}
161+
}
162+
que.add(s);
163+
while (!que.isEmpty()) {
164+
Vertex act = que.poll();
165+
for (Edge e : act.edges) {
166+
if (!e.to.visited && e.revertedEdge.c > e.revertedEdge.f) {
167+
e.to.h = act.h + 1;
168+
que.add(e.to);
169+
e.to.visited = true;
170+
}
171+
}
172+
}
173+
}
174+
175+
private void init() {
176+
177+
for (Edge e : s.edges) {
178+
e.f = e.c;
179+
e.revertedEdge.f = -e.f;
180+
e.to.excess += e.f;
181+
if (e.to != s && e.to != t) {
182+
q.add(e.to);
183+
}
184+
}
185+
recomputeHeigh();
186+
relabelCounter = 0;
187+
}
188+
189+
private void relabel(Vertex v) {
190+
int minimum = 0;
191+
for (Edge e : v.edges) {
192+
if (e.f < e.c) {
193+
minimum = Math.min(minimum, e.to.h);
194+
}
195+
}
196+
v.h = minimum + 1;
197+
}
198+
199+
private void push(Vertex u, Edge e) {
200+
long delta = (u.excess < e.c - e.f) ? u.excess : e.c - e.f;
201+
e.f += delta;
202+
e.revertedEdge.f -= delta;
203+
u.excess -= delta;
204+
if (e.to.excess == 0 && e.to != s && e.to != t) {
205+
q.add(e.to);
206+
}
207+
e.to.excess += delta;
208+
}
209+
210+
211+
private void discharge(Vertex u) {
212+
while (u.excess > 0) {
213+
if (u.currentEdge == u.edges.size()) {
214+
relabel(u);
215+
if ((++relabelCounter) == n) {
216+
recomputeHeigh();
217+
for (Vertex vertex : vertices) {
218+
vertex.currentEdge = 0;
219+
}
220+
relabelCounter = 0;
221+
}
222+
u.currentEdge = 0;
223+
} else {
224+
Edge e = u.edges.get(u.currentEdge);
225+
if (e.f < e.c && u.h == e.to.h + 1) {
226+
push(u, e);
227+
} else u.currentEdge++;
228+
}
229+
}
230+
}
231+
232+
private long maxFlow() {
233+
init();
234+
while (!q.isEmpty()) {
235+
discharge(q.poll());
236+
}
237+
return t.excess;
238+
}
239+
240+
}

‎test/com/jwetherell/algorithms/graph/test/PushRelabelTest.java‎

Lines changed: 53 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,53 @@
1+
package com.jwetherell.algorithms.graph.test;
2+
3+
import com.jwetherell.algorithms.data_structures.Graph;
4+
import com.jwetherell.algorithms.graph.PushRelabel;
5+
import org.junit.Test;
6+
7+
import java.util.Map;
8+
import java.util.TreeMap;
9+
10+
import static org.junit.Assert.assertTrue;
11+
12+
/**
13+
* @author mrowka
14+
*/
15+
public class PushRelabelTest {
16+
17+
private static class ExampleInput {
18+
19+
final Graph.Vertex<Integer> v1 = new Graph.Vertex<Integer>(1);
20+
final Graph.Vertex<Integer> v2 = new Graph.Vertex<Integer>(2);
21+
final Graph.Vertex<Integer> v3 = new Graph.Vertex<Integer>(3);
22+
final Graph.Vertex<Integer> v4 = new Graph.Vertex<Integer>(4);
23+
24+
final Map<Graph.Edge<Integer>, Long> capacities = new TreeMap<Graph.Edge<Integer>, Long>();
25+
final Graph.Edge<Integer> e1_2 = new Graph.Edge<Integer>(1, v1, v2);
26+
final Graph.Edge<Integer> e1_3 = new Graph.Edge<Integer>(1, v1, v3);
27+
final Graph.Edge<Integer> e2_3 = new Graph.Edge<Integer>(1, v2, v3);
28+
final Graph.Edge<Integer> e3_2 = new Graph.Edge<Integer>(1, v3, v2);
29+
final Graph.Edge<Integer> e2_4 = new Graph.Edge<Integer>(1, v2, v4);
30+
final Graph.Edge<Integer> e3_4 = new Graph.Edge<Integer>(1, v3, v4);
31+
32+
{
33+
capacities.put(e1_2, 3L);
34+
capacities.put(e1_3, 5L);
35+
capacities.put(e3_2, 3L);
36+
capacities.put(e2_3, 2L);
37+
capacities.put(e2_4, 7L);
38+
capacities.put(e3_4, 1L);
39+
}
40+
41+
42+
final Graph.Vertex<Integer> source = v1;
43+
final Graph.Vertex<Integer> sink = v4;
44+
45+
}
46+
47+
48+
@Test
49+
public void testPushRelabel() {
50+
ExampleInput exampleInput = new ExampleInput();
51+
assertTrue(PushRelabel.getMaximumFlow(exampleInput.capacities, exampleInput.source, exampleInput.sink) == 7);
52+
}
53+
}

0 commit comments

Comments
 (0)