编程练习（二）

题目：字符串"aa bb cc dd ee ff hh ii" 每个元素以空格隔开，从这个字符串中随机选择5个输出，要求输出的元素必须符合元素在字符串先后位置，例如输出aa bb cc dd ee 、 aa bb dd ff ii 等等.

解决思路： 递归实现排序组合

实现代码：

public class AnotherCombinationTest {
	private static final String str = "aa bb cc dd ee ff hh ii";
	
	public static void main(String args[]) {
		int len = 5;
		String[] inArrays = str.split(" ");
		String[] outArrays = new String[len];
		go(1, inArrays, outArrays);
	}
	
	private static void go(int level, String[] inArrays, String[] outArrays) {
		List<String> inList = new ArrayList<String>();
		for (int i = 0; i < inArrays.length; i++) {
			String _temp = inArrays[i];
			if (inList.contains(_temp)) continue;
			inList.add(_temp);
			outArrays[level - 1] = _temp;
			int nextLevel = level + 1;
			if (level == 5) {
				System.out.println(Arrays.toString(outArrays));
			} else {
				go(nextLevel, createNewArray(inArrays, i + 1), outArrays);
			}
		}
	}
	
	/**
	 * 构建新的待排序选择数组
	 * @param oldArray
	 * @param index 已经被选择的元素之前的元素将全部被剔除
	 * @return
	 */
	private static String[] createNewArray(String[] oldArray, int index) {
		String[] newArray = new String[oldArray.length - index];
		for (int i = 0; i < oldArray.length; i++) {
			if (i < index) continue;
			newArray[i - index] = oldArray[i];
		}
		return newArray;
	}
	
	
}