Java List Include getPrefixesAndSuffixes(List items, int minSize, int maxSize, T paddingSymbol, boolean includePrefixes, boolean includeSuffixes)

Description

Get all prefix/suffix combinations from a list.

License

Open Source License

Parameter

Parameter	Description
T	The type of items contained in the list.
items	The list of items.
minSize	The minimum length of a prefix/suffix span (should be at least 1)
maxSize	The maximum length of a prefix/suffix span
paddingSymbol	Symbol to be included if we run out of bounds (e.g. if items has size 3 and we try to extract a span of length 4).
includePrefixes	Whether to extract prefixes
includeSuffixes	Whether to extract suffixes

Return

All prefix/suffix combinations of the given sizes.

Declaration

public static <T> List<List<T>> getPrefixesAndSuffixes(List<T> items, int minSize, int maxSize, T paddingSymbol,
        boolean includePrefixes, boolean includeSuffixes) 

Method Source Code

//package com.java2s;

import java.util.*;

public class Main {
    /**//from   w  w w  .  j  a  v a 2  s .c o  m
     * Get all prefix/suffix combinations from a list. It can extract just
     * prefixes, just suffixes, or prefixes and suffixes of the same length.
     *
     * For example:
     *
     * <pre>
     * List&lt;String&gt; items = Arrays.asList(&quot;a&quot;, &quot;b&quot;, &quot;c&quot;, &quot;d&quot;);
     * System.out.println(CollectionUtils.getPrefixesAndSuffixes(items, 1, 2, null, true, true));
     * </pre>
     *
     * would print out:
     *
     * <pre>
     * [[d], [a], [a, d], [d, c], [a, b], [a, b, c, d]]
     * </pre>
     *
     * and
     *
     * <pre>
     * List&lt;String&gt; items2 = Arrays.asList(&quot;a&quot;);
     * System.out.println(CollectionUtils.getPrefixesAndSuffixes(items2, 1, 2, null, true, true));
     * </pre>
     *
     * would print:
     *
     * <pre>
     * [[a], [a], [a, a], [a, null], [a, null], [a, null, a, null]]
     * </pre>
     *
     * @param <T> The type of items contained in the list.
     * @param items The list of items.
     * @param minSize The minimum length of a prefix/suffix span (should be at least 1)
     * @param maxSize The maximum length of a prefix/suffix span
     * @param paddingSymbol Symbol to be included if we run out of bounds (e.g. if items has
     *          size 3 and we try to extract a span of length 4).
     * @param includePrefixes Whether to extract prefixes
     * @param includeSuffixes Whether to extract suffixes
     * @return All prefix/suffix combinations of the given sizes.
     */
    public static <T> List<List<T>> getPrefixesAndSuffixes(List<T> items, int minSize, int maxSize, T paddingSymbol,
            boolean includePrefixes, boolean includeSuffixes) {
        assert minSize > 0;
        assert maxSize >= minSize;
        assert includePrefixes || includeSuffixes;

        List<List<T>> prefixesAndSuffixes = new ArrayList<>();
        for (int span = minSize - 1; span < maxSize; span++) {
            List<Integer> indices = new ArrayList<>();
            List<T> seq = new ArrayList<>();
            if (includePrefixes) {
                for (int i = 0; i <= span; i++) {
                    indices.add(i);
                }
            }
            if (includeSuffixes) {
                int maxIndex = items.size() - 1;
                for (int i = span; i >= 0; i--) {
                    indices.add(maxIndex - i);
                }
            }

            for (int i : indices) {
                try {
                    seq.add(items.get(i));
                } catch (IndexOutOfBoundsException ioobe) {
                    seq.add(paddingSymbol);
                }
            }

            prefixesAndSuffixes.add(seq);
        }

        return prefixesAndSuffixes;
    }
}

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