/**

 * 	有一个字符串，根据输入参数m，找出字符串的m个字符的所有字符串

	例如：

	String str ="abc", m=2  得到结果是 "ab" "ac" "bc"

	String str ="abcd" , m=3 得到结果是"abc" "acd" "bcd" "abd"

	注：程序摘自网上

 *

 */

public static void main(String[] args) {

		List<String> list = choose("abcde",3);

		for (String string : list) {

			System.out.println(string);

		}

	}

	public static List<String> choose(String target, int m) {

		List<String> resultList = new LinkedList<>();

		doChoose(resultList, target, "", m, 0);

		return resultList;

	}

	private static void doChoose(List<String> resultList, String target,

			String resultStr, int m, int head) {

		// 递归头

		if (resultStr.length() == m) {

			resultList.add(resultStr);

			return;

		}

		// 递归体

		for (int i = head; i < target.length(); i++) {

			doChoose(resultList, target, resultStr + target.charAt(i), m, i + 1);

		}

	}