最小连续(周一周二周三，就显示周一至周三)

 有一需求,选中周期后,显示规则
 * 周一周二周三，就显示周一至周三，
 * 周一周二周三周五，显示“周一至周三、周五”
 * 周一周三周五，显示“周一、周三、周五”

    public class PairX<F, S> {
    public F first;
    public S second;

    /**
     * Constructor for a Pair.
     *
     * @param first  the first object in the Pair
     * @param second the second object in the pair
     */
    public PairX(F first, S second) {
        this.first = first;
        this.second = second;
    }
  }

    /**
     * 周一周二周三，就显示周一至周三，
     * 周一周二周三周五，显示“周一至周三、周五”
     * 周一周三周五，显示“周一、周三、周五”
     *
     * @param tartget
     * @param sb
     */
    public static void format(List<PairX<Integer, String>> tartget, StringBuilder sb) {
        if (tartget == null || sb == null) {
            return;
        }
        int stub = -1;
        while (!tartget.isEmpty()) {
            PairX<Integer, String> first = tartget.get(0);
            Integer end = first.first;
            for (int i = 1; i < tartget.size(); i++) {
                PairX<Integer, String> sub = tartget.get(i);
                end += 1;
                if (end == sub.first) {
                    stub = i;
                } else {
                    break;
                }
            }
            if (stub == -1) {
                sb.append(first.second + ",");
                tartget.remove(0);
            } else {
                sb.append(first.second + "至" + tartget.get(stub).second + ",");
                if (stub == tartget.size() - 1) {
                    tartget.clear();
                } else {
                    tartget = new ArrayList<>(tartget.subList(stub + 1, tartget.size()));
                }
            }
            stub = -1;
        }
        String s = sb.toString();
        if (!isEmpty(s)) {
            boolean b = s.endsWith(",");
            if (b) {
                sb.setLength(sb.length() - 1);
            }
        }
    }
    //TextUtils.isEmpty(s)是android的 ,源码复制出来
    public static boolean isEmpty(@Nullable CharSequence str) {
        return str == null || str.length() == 0;
    }

    //注意target需要是排序后的 
    public static void main(String[] args) {

        String s = "123";
        StringBuilder sb = new StringBuilder();
        List<PairX<Integer, String>> tartget = new ArrayList();
        tartget.add(PairX.create(0, "周一"));
        tartget.add(PairX.create(1, "周二"));
        tartget.add(PairX.create(2, "周三"));
        tartget.add(PairX.create(3, "周四"));
        tartget.add(PairX.create(4, "周五"));
        tartget.add(PairX.create(5, "周六"));
        tartget.add(PairX.create(6, "周日"));
        format(tartget, sb);
        System.out.println(sb.toString());
        tartget = new ArrayList();
        sb = new StringBuilder();
        tartget.add(PairX.create(0, "周一"));
        tartget.add(PairX.create(1, "周二"));
        tartget.add(PairX.create(2, "周三"));
        tartget.add(PairX.create(3, "周四"));
        tartget.add(PairX.create(5, "周六"));
        tartget.add(PairX.create(6, "周日"));
        format(tartget, sb);
        System.out.println(sb.toString());
// ==================符合预期==================
//                周一至周日
//                周一至周四,周六至周日
    }