Feb
21

Binomial coefficient using generic Typ

With generic typ List

/**
	 * random Sampling without repeat (Binomail coefficient: n choose m)
	 * 
	 * @param items
	 *            A list with basic Data
	 * @param m
	 *            the number of desired Samples
	 * @param seed
	 *            the initial seed
	 * @return A list with obtained Samples
	 */
	public static <E> List<E> randomSample(List<E> items, int m, long seed) {

		if (m > items.size()) {
			System.err.println("m should smaller than the items.size():"
					+ items.size());
			System.exit(-1);
		}

		Random rnd = new Random(seed);
		for (int i = 0; i < m; i++) {
			int pos = i + rnd.nextInt(items.size() - i);
			E tmp = items.get(pos);
			items.set(pos, items.get(i));
			items.set(i, tmp);
		}

		return items.subList(0, m);
	}

With generic typ Array

	/**
	 * random Sampling without repeat
	 * 
	 * @param items
	 *            An array with basic Data
	 * @param m
	 *            the number of desired Samples
	 * @param seed
	 *            the initial seed
	 * @return A array with obtained Samples
	 */
	public static <E> E[] randomSample2(E[] items, int m, long seed){
		
		if (m > items.length) {
			System.err.println("m should smaller than the items.size():"
					+ items.length);
			System.exit(-1);
		}else if (items.length <=1) {
			System.err.println("items can't be empty"
					+ items.length);
			System.exit(-1);
		}
		
		Random rnd = new Random(seed);
		for (int i = 0; i < m; i++) {
			int pos = i + rnd.nextInt(items.length - i);
			E tmp = items[pos];
			items[pos] = items[i];
			items[i] = tmp;
		}
		
		E[] result = Arrays.copyOf(items, m);
		
		return result;
		
	}

Written by connygy. Posted in java

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