199999+29999+3999+499+59
=200000+30000+4000+500+60-5
=234560-5
=234555
100+99-98-97+96+95-94-93+.+8+7-6-5+4+3-2-1
=100+（99-98-97+96)+(95-94-93+92)+.+(7-6-5+4)+(3-2-1)
=100+0+0+……+0+0
=100