101 lines
3.1 KiB
Java
101 lines
3.1 KiB
Java
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import edu.princeton.cs.introcs.StdIn;
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import edu.princeton.cs.introcs.StdOut;
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/*************************************************************************
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* Compilation: javac CPM.java
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* Execution: java CPM < input.txt
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* Dependencies: EdgeWeightedDigraph.java AcyclicDigraphLP.java StdOut.java
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* Data files: http://algs4.cs.princeton.edu/44sp/jobsPC.txt
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*
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* Critical path method.
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*
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* % java CPM < jobsPC.txt
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* job start finish
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* --------------------
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* 0 0.0 41.0
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* 1 41.0 92.0
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* 2 123.0 173.0
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* 3 91.0 127.0
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* 4 70.0 108.0
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* 5 0.0 45.0
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* 6 70.0 91.0
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* 7 41.0 73.0
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* 8 91.0 123.0
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* 9 41.0 70.0
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* Finish time: 173.0
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*
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*************************************************************************/
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/**
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* The CPM class provides a client that solves the
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* parallel precedence-constrained job scheduling problem
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* via the critical path method . It reduces the problem
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* to the longest-paths problem in edge-weighted DAGs.
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* It builds an edge-weighted digraph (which must be a DAG)
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* from the job-scheduling problem specification,
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* finds the longest-paths tree, and computes the longest-paths
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* lengths (which are precisely the start times for each job).
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*
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* This implementation uses {@link AcyclicLP} to find a longest
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* path in a DAG.
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* The running time is proportional to V + E ,
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* where V is the number of jobs and E is the
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* number of precedence constraints.
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*
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* For additional documentation,
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* see <a href="http://algs4.cs.princeton.edu/44sp">Section 4.4</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 CPM {
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// this class cannot be instantiated
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private CPM() { }
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/**
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* Reads the precedence constraints from standard input
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* and prints a feasible schedule to standard output.
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*/
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public static void main(String[] args) {
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// number of jobs
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int N = StdIn.readInt();
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// source and sink
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int source = 2*N;
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int sink = 2*N + 1;
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// build network
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EdgeWeightedDigraph G = new EdgeWeightedDigraph(2*N + 2);
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for (int i = 0; i < N; i++) {
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double duration = StdIn.readDouble();
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G.addEdge(new DirectedEdge(source, i, 0.0));
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G.addEdge(new DirectedEdge(i+N, sink, 0.0));
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G.addEdge(new DirectedEdge(i, i+N, duration));
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// precedence constraints
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int M = StdIn.readInt();
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for (int j = 0; j < M; j++) {
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int precedent = StdIn.readInt();
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G.addEdge(new DirectedEdge(N+i, precedent, 0.0));
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}
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}
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// compute longest path
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AcyclicLP lp = new AcyclicLP(G, source);
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// print results
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StdOut.println(" job start finish");
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StdOut.println("--------------------");
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for (int i = 0; i < N; i++) {
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StdOut.printf("%4d %7.1f %7.1f\n", i, lp.distTo(i), lp.distTo(i+N));
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}
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StdOut.printf("Finish time: %7.1f\n", lp.distTo(sink));
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}
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}
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