Write 1,2,3,4,5,6,7,8,9,10,11,12 to the 1999 digit in turn to form the 1999 digit. What is the remainder of this number divided by 9?

Write 1,2,3,4,5,6,7,8,9,10,11,12 to the 1999 digit in turn to form the 1999 digit. What is the remainder of this number divided by 9?

One digit, nine, nine
Two digits, 90 digits, 180 digits
Three digits, 900, 2700
Therefore, the number of 1999 digits is composed of 1810 3 digits and all 1 and 2 digits. Let X be the last digit
Then 1810 / 3 = X-100 + 1, x = 702.33333, that is, the last number is incomplete, x = 703, actually only 70 is written, but 3 is not written
The sum of all 1-digit numbers is 45, the sum of 2-digit numbers is 855, and the sum of 3-digit numbers is 8031
Then the sum of all numbers is 8931, which can be divided by 3 and 2977
So the 1999 digit, the single digit is 0, can be divided by 3
2 977 divided by 3 was 992.3333
So the number is divided into 9 and 3