P12.java

package com.shekhargulati.ninetynine_problems._01_lists;

import java.util.AbstractMap.SimpleEntry;
import java.util.Collections;
import java.util.List;
import java.util.stream.Stream;

import static java.util.stream.Collectors.toList;

/**
 * <b>(**) Decode a run-length encoded list.</b>
 * <pre>
 *     decode(Arrays.asList((4, "a"), "b", (2, "c"), (2, "a"), "d", (4, "e")))
 * </pre>
 */
public class P12 {

    public static <T> List<T> decode(List<Object> encoded) {
        return encoded.stream().flatMap(e -> {
            if (e instanceof SimpleEntry) {
                SimpleEntry<Integer, T> entry = (SimpleEntry<Integer, T>) e;
                return Collections.nCopies(entry.getKey(), entry.getValue()).stream();
            }
            return Stream.of((T) e);
        }).collect(toList());
    }
}