146 lines
4.6 KiB
Java
146 lines
4.6 KiB
Java
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import edu.princeton.cs.introcs.In;
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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 SymbolDigraph.java
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* Execution: java SymbolDigraph
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* Dependencies: ST.java Digraph.java In.java
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*
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* % java SymbolDigraph routes.txt " "
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* JFK
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* MCO
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* ATL
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* ORD
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* ATL
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* HOU
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* MCO
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* LAX
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*
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*************************************************************************/
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/**
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* The SymbolDigraph class represents a digraph, where the
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* vertex names are arbitrary strings.
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* By providing mappings between string vertex names and integers,
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* it serves as a wrapper around the
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* {@link Digraph} data type, which assumes the vertex names are integers
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* between 0 and V - 1.
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* It also supports initializing a symbol digraph from a file.
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*
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* This implementation uses an {@link ST} to map from strings to integers,
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* an array to map from integers to strings, and a {@link Digraph} to store
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* the underlying graph.
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* The index and contains operations take time
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* proportional to log V , where V is the number of vertices.
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* The name operation takes constant time.
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*
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* For additional documentation, see <a href="http://algs4.cs.princeton.edu/42digraph">Section 4.2</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 SymbolDigraph {
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private ST<String, Integer> st; // string -> index
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private String[] keys; // index -> string
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private Digraph G;
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/**
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* Initializes a digraph from a file using the specified delimiter.
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* Each line in the file contains
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* the name of a vertex, followed by a list of the names
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* of the vertices adjacent to that vertex, separated by the delimiter.
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* @param filename the name of the file
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* @param delimiter the delimiter between fields
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*/
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public SymbolDigraph(String filename, String delimiter) {
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st = new ST<String, Integer>();
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// First pass builds the index by reading strings to associate
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// distinct strings with an index
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In in = new In(filename);
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while (in.hasNextLine()) {
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String[] a = in.readLine().split(delimiter);
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for (int i = 0; i < a.length; i++) {
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if (!st.contains(a[i]))
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st.put(a[i], st.size());
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}
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}
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// inverted index to get string keys in an aray
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keys = new String[st.size()];
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for (String name : st.keys()) {
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keys[st.get(name)] = name;
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}
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// second pass builds the digraph by connecting first vertex on each
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// line to all others
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G = new Digraph(st.size());
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in = new In(filename);
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while (in.hasNextLine()) {
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String[] a = in.readLine().split(delimiter);
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int v = st.get(a[0]);
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for (int i = 1; i < a.length; i++) {
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int w = st.get(a[i]);
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G.addEdge(v, w);
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}
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}
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}
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/**
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* Does the digraph contain the vertex named s ?
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* @param s the name of a vertex
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* @return true if s is the name of a vertex, and false otherwise
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*/
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public boolean contains(String s) {
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return st.contains(s);
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}
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/**
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* Returns the integer associated with the vertex named s .
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* @param s the name of a vertex
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* @return the integer (between 0 and V - 1) associated with the vertex named s
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*/
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public int index(String s) {
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return st.get(s);
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}
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/**
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* Returns the name of the vertex associated with the integer v .
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* @param v the integer corresponding to a vertex (between 0 and V - 1)
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* @return the name of the vertex associated with the integer v
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*/
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public String name(int v) {
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return keys[v];
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}
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/**
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* Returns the digraph assoicated with the symbol graph. It is the client's responsibility
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* not to mutate the digraph.
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* @return the digraph associated with the symbol digraph
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*/
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public Digraph G() {
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return G;
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}
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/**
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* Unit tests the SymbolDigraph data type.
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*/
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public static void main(String[] args) {
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String filename = args[0];
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String delimiter = args[1];
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SymbolDigraph sg = new SymbolDigraph(filename, delimiter);
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Digraph G = sg.G();
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while (!StdIn.isEmpty()) {
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String t = StdIn.readLine();
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for (int v : G.adj(sg.index(t))) {
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StdOut.println(" " + sg.name(v));
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}
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}
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}
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}
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