sequence of numbers 1 to 3999 written like ( 123456789101112......3999) . Find the number of zeros in this sequence ?

Question

Can you find a seven digit number which describes itself.

The first digit is the number of zeros in the number.
The second digit is the number of ones in the number, etc.

For example, in the number 21200, there are 2 zeros, 1 one, 2 twos, 0 threes and 0 fours.

Answer 1

Let me put in this way, its a permutation combination question with following parts
number of zeros from
1-9
10-99
101-999
1000-3999

For the first case the answer is 0
For the second case answer is [1-9]0 so 9
For the third case [1-9]0[0-9] + [1-9][0-9]0 = 9*1*10+9*10*1 = 180
For the third case [1-3]0[0-9][0-9]+[1-3][0-9]0[0-9]+[1-3][0-9][0-9]0 = 300+300+300 = 900

Total: 900+180+9 = 1089

Python Code

def countZeros(n):
    result = 0
    i = 1

    while True:
        b, c = divmod(n, i)
        a, b = divmod(b, 10)

        if a == 0:
            return result

        if b == 0:
            result += (a - 1) * i + c + 1
        else:
            result += a * i

        i *= 10

print countZeros(3999)

Answer 2

there are 400