problem-oj4

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#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
给定一个仅包含整数，且按照大小顺序排好序的列表，列表内不存在重复的整数。
实现一个函数，将列表格式化为由`,`(逗号)分隔的字符串；如果相邻的整数(至少3个)是
连续的(值相差1为连续)，则将这几个相邻的整数格式化为由`-`(减号)分隔、左右分别为
起始和终止位整数的字符串。

示例：
func([-6,-3,-2,-1,0,1,3,4,5,7,8,9,10,11,14,15,17,18,19,20])  -->  '-6,-3-1,3-5,7-11,14,15,17-20'
func([-3,-2,-1,2,10,15,16,18,19,20])  -->  '-3--1,2,10,15,16,18-20'

特殊情况示例：
func([])  -->  ''
"""

import unittest
from itertools import groupby


def func(lst):
    # your code
    sum = sub_arr(lst)
    return ','.join(sum)


def sub_arr(lst):
    fun = lambda x: x[1] - x[0]
    sum = []
    for k, g in groupby(enumerate(lst), fun):
        s = [v for i, v in g]
#        print(s)
        if len(s) <= 1:
            sum.append(str(s[0]))
        elif len(s) == 2:
            sum.append(str(s[0]))
            sum.append(str(s[1]))
        else:
            target = [str(s[0]), str(s[-1])]
            n = '-'.join(target)
            sum.append(n)

    return sum


class DefaultTestCase(unittest.TestCase):

    def test_func(self):
        self.assertEqual(func([-6,-3,-2,-1,0,1,3,4,5,7,8,9,10,11,14,15,17,18,19,20]), '-6,-3-1,3-5,7-11,14,15,17-20')
        self.assertEqual(func([-3,-2,-1,2,10,15,16,18,19,20]), '-3--1,2,10,15,16,18-20')
        self.assertEqual(func([]), '')
        self.assertEqual(func([-6,-4,-2,0,2,4,6]), '-6,-4,-2,0,2,4,6')
        self.assertEqual(func([-6,-5,-3,-2,0,1,3,4,6]), '-6,-5,-3,-2,0,1,3,4,6')

if __name__ == '__main__':
    unittest.main()