194 lines
7.2 KiB
Java
194 lines
7.2 KiB
Java
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import edu.princeton.cs.introcs.StdOut;
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/*************************************************************************
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* Compilation: javac FlowEdge.java
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* Execution: java FlowEdge
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*
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* Capacitated edge with a flow in a flow network.
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*
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*************************************************************************/
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/**
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* The FlowEdge class represents a capacitated edge with a
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* flow in a {@link FlowNetwork}. Each edge consists of two integers
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* (naming the two vertices), a real-valued capacity, and a real-valued
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* flow. The data type provides methods for accessing the two endpoints
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* of the directed edge and the weight. It also provides methods for
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* changing the amount of flow on the edge and determining the residual
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* capacity of the edge.
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*
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* For additional documentation, see <a href="http://algs4.cs.princeton.edu/64maxflow">Section 6.4</a> of
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* Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne.
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*
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* @author Robert Sedgewick
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* @author Kevin Wayne
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*/
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public class FlowEdge {
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private final int v; // from
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private final int w; // to
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private final double capacity; // capacity
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private double flow; // flow
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/**
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* Initializes an edge from vertex v to vertex w with
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* the given capacity and zero flow.
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* @param v the tail vertex
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* @param w the head vertex
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* @param capacity the capacity of the edge
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* @throws java.lang.IndexOutOfBoundsException if either v or w
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* is a negative integer
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* @throws java.lang.IllegalArgumentException if capacity is negative
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*/
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public FlowEdge(int v, int w, double capacity) {
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if (v < 0) throw new IndexOutOfBoundsException("Vertex name must be a nonnegative integer");
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if (w < 0) throw new IndexOutOfBoundsException("Vertex name must be a nonnegative integer");
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if (!(capacity >= 0.0)) throw new IllegalArgumentException("Edge capacity must be nonnegaitve");
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this.v = v;
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this.w = w;
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this.capacity = capacity;
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this.flow = 0.0;
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}
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/**
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* Initializes an edge from vertex v to vertex w with
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* the given capacity and flow .
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* @param v the tail vertex
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* @param w the head vertex
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* @param capacity the capacity of the edge
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* @param flow the flow on the edge
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* @throws java.lang.IndexOutOfBoundsException if either v or w
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* is a negative integer
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* @throws java.lang.IllegalArgumentException if capacity is negative
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* @throws java.lang.IllegalArgumentException unless flow is between
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* 0.0 and capacity .
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*/
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public FlowEdge(int v, int w, double capacity, double flow) {
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if (v < 0) throw new IndexOutOfBoundsException("Vertex name must be a nonnegative integer");
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if (w < 0) throw new IndexOutOfBoundsException("Vertex name must be a nonnegative integer");
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if (!(capacity >= 0.0)) throw new IllegalArgumentException("Edge capacity must be nonnegaitve");
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if (!(flow <= capacity)) throw new IllegalArgumentException("Flow exceeds capacity");
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if (!(flow >= 0.0)) throw new IllegalArgumentException("Flow must be nonnnegative");
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this.v = v;
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this.w = w;
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this.capacity = capacity;
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this.flow = flow;
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}
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/**
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* Initializes a flow edge from another flow edge.
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* @param e the edge to copy
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*/
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public FlowEdge(FlowEdge e) {
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this.v = e.v;
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this.w = e.w;
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this.capacity = e.capacity;
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this.flow = e.flow;
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}
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/**
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* Returns the tail vertex of the edge.
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* @return the tail vertex of the edge
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*/
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public int from() {
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return v;
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}
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/**
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* Returns the head vertex of the edge.
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* @return the head vertex of the edge
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*/
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public int to() {
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return w;
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}
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/**
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* Returns the capacity of the edge.
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* @return the capacity of the edge
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*/
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public double capacity() {
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return capacity;
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}
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/**
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* Returns the flow on the edge.
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* @return the flow on the edge
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*/
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public double flow() {
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return flow;
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}
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/**
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* Returns the endpoint of the edge that is different from the given vertex
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* (unless the edge represents a self-loop in which case it returns the same vertex).
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* @param vertex one endpoint of the edge
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* @return the endpoint of the edge that is different from the given vertex
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* (unless the edge represents a self-loop in which case it returns the same vertex)
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* @throws java.lang.IllegalArgumentException if vertex is not one of the endpoints
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* of the edge
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*/
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public int other(int vertex) {
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if (vertex == v) return w;
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else if (vertex == w) return v;
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else throw new IllegalArgumentException("Illegal endpoint");
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}
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/**
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* Returns the residual capacity of the edge in the direction
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* to the given vertex .
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* @param vertex one endpoint of the edge
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* @return the residual capacity of the edge in the direction to the given vertex
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* If vertex is the tail vertex, the residual capacity equals
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* capacity() - flow() ; if vertex is the head vertex, the
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* residual capacity equals flow() .
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* @throws java.lang.IllegalArgumentException if vertex is not one of the endpoints
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* of the edge
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*/
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public double residualCapacityTo(int vertex) {
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if (vertex == v) return flow; // backward edge
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else if (vertex == w) return capacity - flow; // forward edge
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else throw new IllegalArgumentException("Illegal endpoint");
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}
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/**
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* Increases the flow on the edge in the direction to the given vertex.
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* If vertex is the tail vertex, this increases the flow on the edge by delta ;
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* if vertex is the head vertex, this decreases the flow on the edge by delta .
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* @param vertex one endpoint of the edge
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* @throws java.lang.IllegalArgumentException if vertex is not one of the endpoints
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* of the edge
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* @throws java.lang.IllegalArgumentException if delta makes the flow on
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* on the edge either negative or larger than its capacity
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* @throws java.lang.IllegalArgumentException if delta is NaN
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*/
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public void addResidualFlowTo(int vertex, double delta) {
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if (vertex == v) flow -= delta; // backward edge
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else if (vertex == w) flow += delta; // forward edge
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else throw new IllegalArgumentException("Illegal endpoint");
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if (Double.isNaN(delta)) throw new IllegalArgumentException("Change in flow = NaN");
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if (!(flow >= 0.0)) throw new IllegalArgumentException("Flow is negative");
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if (!(flow <= capacity)) throw new IllegalArgumentException("Flow exceeds capacity");
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}
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/**
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* Returns a string representation of the edge.
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* @return a string representation of the edge
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*/
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@Override
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public String toString() {
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return v + "->" + w + " " + flow + "/" + capacity;
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}
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/**
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* Unit tests the FlowEdge data type.
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*/
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public static void main(String[] args) {
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FlowEdge e = new FlowEdge(12, 23, 3.14);
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StdOut.println(e);
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}
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}
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