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## org.apache.lucene.util.fst
Class Util

    java.lang.Object
      org.apache.lucene.util.fst.Util

    public final class Util

extends Object

Static helper methods.

WARNING: This API is experimental and might change in incompatible ways in the next release.

Nested Class Summary
`static class` | `Util.MinResult<T>` Holds a single input (IntsRef) + output, returned by `shortestPaths()`.
`static class` | `Util.TopNSearcher<T>` Utility class to find top N shortest paths from start point(s).

Method Summary
`static
`<T> T`
` | `get(FST<T> fst, BytesRef input)` Looks up the output for this input, or null if the input is not accepted
`static
`<T> T`
` | `get(FST<T> fst, IntsRef input)` Looks up the output for this input, or null if the input is not accepted.
`static IntsRef` | `getByOutput(FST<Long> fst, long targetOutput)` Reverse lookup (lookup by output instead of by input), in the special case when your FSTs outputs are strictly ascending.
`static IntsRef` | `getByOutput(FST<Long> fst, long targetOutput, FST.BytesReader in, FST.Arc<Long> arc, FST.Arc<Long> scratchArc, IntsRef result)` Expert: like `getByOutput(FST, long)` except reusing BytesReader, initial and scratch Arc, and result.
`static
`<T> FST.Arc<T>`
` | `readCeilArc(int label, FST<T> fst, FST.Arc<T> follow, FST.Arc<T> arc, FST.BytesReader in)` Reads the first arc greater or equal that the given label into the provided arc in place and returns it iff found, otherwise return `null`.
`static
`<T> Util.MinResult<T>[]`
` | `shortestPaths(FST<T> fst, FST.Arc<T> fromNode, T startOutput, Comparator<T> comparator, int topN, boolean allowEmptyString)` Starting from node, find the top N min cost completions to a final node.
`static BytesRef` | `toBytesRef(IntsRef input, BytesRef scratch)` Just converts IntsRef to BytesRef; you must ensure the int values fit into a byte.
`static
`<T> void`
` | `toDot(FST<T> fst, Writer out, boolean sameRank, boolean labelStates)` Dumps an `FST` to a GraphViz's `dot` language description for visualization.
`static IntsRef` | `toIntsRef(BytesRef input, IntsRef scratch)` Just takes unsigned byte values from the BytesRef and converts into an IntsRef.
`static IntsRef` | `toUTF16(CharSequence s, IntsRef scratch)` Just maps each UTF16 unit (char) to the ints in an IntsRef.
`static IntsRef` | `toUTF32(char[] s, int offset, int length, IntsRef scratch)` Decodes the Unicode codepoints from the provided char[] and places them in the provided scratch IntsRef, which must not be null, returning it.
`static IntsRef` | `toUTF32(CharSequence s, IntsRef scratch)` Decodes the Unicode codepoints from the provided CharSequence and places them in the provided scratch IntsRef, which must not be null, returning it.

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Method Detail

### get

    public static <T> T get(FST<T> fst,
                            IntsRef input)
                 throws IOException

  Looks up the output for this input, or null if the input is not accepted.

  Throws:
    `IOException`

### get

    public static <T> T get(FST<T> fst,
                            BytesRef input)
                 throws IOException

  Looks up the output for this input, or null if the input is not accepted

  Throws:
    `IOException`

### getByOutput

    public static IntsRef getByOutput(FST<Long> fst,
                                      long targetOutput)
                               throws IOException

  Reverse lookup (lookup by output instead of by input), in the special case when your FSTs outputs are strictly ascending. This locates the input/output pair where the output is equal to the target, and will return null if that output does not exist.

  NOTE: this only works with `FST<Long>`, only works when the outputs are ascending in order with the inputs and only works when you shared the outputs (pass doShare=true to `PositiveIntOutputs.getSingleton()`). For example, simple ordinals (0, 1, 2, ...), or file offets (when appending to a file) fit this.

  Throws:
    `IOException`

### getByOutput

    public static IntsRef getByOutput(FST<Long> fst,
                                      long targetOutput,
                                      FST.BytesReader in,
                                      FST.Arc<Long> arc,
                                      FST.Arc<Long> scratchArc,
                                      IntsRef result)
                               throws IOException

  Expert: like `getByOutput(FST, long)` except reusing BytesReader, initial and scratch Arc, and result.

  Throws:
    `IOException`

### shortestPaths

    public static <T> Util.MinResult<T>[] shortestPaths(FST<T> fst,
                                                        FST.Arc<T> fromNode,
                                                        T startOutput,
                                                        Comparator<T> comparator,
                                                        int topN,
                                                        boolean allowEmptyString)
                                             throws IOException

  Starting from node, find the top N min cost completions to a final node.

  NOTE: you must share the outputs when you build the FST (pass doShare=true to `PositiveIntOutputs.getSingleton()`).

  Throws:
    `IOException`

### toDot

    public static <T> void toDot(FST<T> fst,
                                 Writer out,
                                 boolean sameRank,
                                 boolean labelStates)
                      throws IOException

  Dumps an `FST` to a GraphViz's `dot` language description for visualization. Example of use:

       PrintWriter pw = new PrintWriter("out.dot");
       Util.toDot(fst, pw, true, true);
       pw.close();

  and then, from command line:

       dot -Tpng -o out.png out.dot

  Note: larger FSTs (a few thousand nodes) won't even render, don't bother. If the FST is > 2.1 GB in size then this method will throw strange exceptions.

  Parameters:
    `sameRank` - If `true`, the resulting `dot` file will try to order states in layers of breadth-first traversal. This may mess up arcs, but makes the output FST's structure a bit clearer.
    `labelStates` - If `true` states will have labels equal to their offsets in their binary format. Expands the graph considerably.
  Throws:
    `IOException`
  See Also:
    "http://www.graphviz.org/"

### toUTF16

    public static IntsRef toUTF16(CharSequence s,
                                  IntsRef scratch)

  Just maps each UTF16 unit (char) to the ints in an IntsRef.

### toUTF32

    public static IntsRef toUTF32(CharSequence s,
                                  IntsRef scratch)

  Decodes the Unicode codepoints from the provided CharSequence and places them in the provided scratch IntsRef, which must not be null, returning it.

### toUTF32

    public static IntsRef toUTF32(char[] s,
                                  int offset,
                                  int length,
                                  IntsRef scratch)

  Decodes the Unicode codepoints from the provided char[] and places them in the provided scratch IntsRef, which must not be null, returning it.

### toIntsRef

    public static IntsRef toIntsRef(BytesRef input,
                                    IntsRef scratch)

  Just takes unsigned byte values from the BytesRef and converts into an IntsRef.

### toBytesRef

    public static BytesRef toBytesRef(IntsRef input,
                                      BytesRef scratch)

  Just converts IntsRef to BytesRef; you must ensure the int values fit into a byte.

### readCeilArc

    public static <T> FST.Arc<T> readCeilArc(int label,
                                             FST<T> fst,
                                             FST.Arc<T> follow,
                                             FST.Arc<T> arc,
                                             FST.BytesReader in)
                                  throws IOException

  Reads the first arc greater or equal that the given label into the provided arc in place and returns it iff found, otherwise return `null`.

  Parameters:
    `label` - the label to ceil on
    `fst` - the fst to operate on
    `follow` - the arc to follow reading the label from
    `arc` - the arc to read into in place
    `in` - the fst's `FST.BytesReader`
  Throws:
    `IOException`

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