Disclaimer: This article is a blogger original article, follow the CC 4.0 BY-SA copyright agreement, reproduced, please attach the original source link and this statement.
Today is what lessons are learned, stroked the English word a day, and made a mathematical exercises, the political order a bit, come back tonight, it is intended to be a water problem, it is a combination of numbers, but ignored the k the size 1e9, combined direct and RE, but in fact because of the small n, 2000, so the number of combinations required for direct cycle can be obtained ,,, but do not want to write, go to bed, and tomorrow continue the spirit of learning!