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package algs64;
import  stdlib.*;

/* ***********************************************************************
 *  Compilation:  javac FlowEdge.java
 *  Execution:    java FlowEdge
 *
 *  Capacitated edge with a flow in a flow network.
 *
 *************************************************************************/

/**
 *  The <tt>FlowEdge</tt> class represents a capacitated edge with a flow
 *  in a digraph.
 *  <p>
 *  For additional documentation, see <a href="/algs4/74or">Section 7.4</a> of
 *  <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
 */


public class FlowEdge {
  private final int v;             // from
  private final int w;             // to
  private final double capacity;   // capacity
  private double flow;             // flow

  public FlowEdge(int v, int w, double capacity) {
    if (capacity < 0) throw new IllegalArgumentException("Negative edge capacity");
    this.v         = v;
    this.w         = w;
    this.capacity  = capacity;
    this.flow      = 0;
  }

  public FlowEdge(int v, int w, double capacity, double flow) {
    if (capacity < 0) throw new IllegalArgumentException("Negative edge capacity");
    this.v         = v;
    this.w         = w;
    this.capacity  = capacity;
    this.flow      = flow;
  }

  // copy constructor
  public FlowEdge(FlowEdge e) {
    this.v         = e.v;
    this.w         = e.w;
    this.capacity  = e.capacity;
    this.flow      = e.flow;
  }

  // accessor methods
  public int from()         { return v;        }
  public int to()           { return w;        }
  public double capacity()  { return capacity; }
  public double flow()      { return flow;     }


  public int other(int vertex) {
    if      (vertex == v) return w;
    else if (vertex == w) return v;
    else throw new IllegalArgumentException("Illegal endpoint");
  }

  public double residualCapacityTo(int vertex) {
    if      (vertex == v) return flow;              // backward edge
    else if (vertex == w) return capacity - flow;   // forward edge
    else throw new IllegalArgumentException("Illegal endpoint");
  }

  public void addResidualFlowTo(int vertex, double delta) {
    if      (vertex == v) flow -= delta;           // backward edge
    else if (vertex == w) flow += delta;           // forward edge
    else throw new IllegalArgumentException("Illegal endpoint");
  }


  public String toString() {
    return v + "->" + w + " " + flow + "/" + capacity;
  }


  /**
   * Test client.
   */
  public static void main(String[] args) {
    FlowEdge e = new FlowEdge(12, 23, 3.14);
    StdOut.println(e);
  }

}