Given an integer N where 1 ≤ N ≤ 105, the task is to find the number of positive integers less than or equal to N that have an odd number of digits without leading zeros.
Input: N = 11
1, 2, 3, …, 8 and 9 are the numbers ≤ 11
with odd number of digits.
Input: N = 893
Naive approach: Traverse from 1 to N and for each number check if it contains odd digits or not.
Efficient approach: For the values:
- When N < 10 then the count of valid numbers will be N.
- When N / 10 < 10 then 9.
- When N / 100 < 10 then 9 + N – 99.
- When N / 1000 < 10 then 9 + 900.
- When N / 10000 < 10 then 909 + N – 9999.
- Otherwise 90909.
Below is the implementation of the above approach:
- Find the smallest positive number which can not be represented by given digits
- Find the number of integers from 1 to n which contains digits 0's and 1's only
- Find the first N integers such that the sum of their digits is equal to 10
- Find a Number X whose sum with its digits is equal to N
- Find a number x such that sum of x and its digits is equal to given n.
- Count of integers in a range which have even number of odd digits and odd number of even digits
- Number of ways in which N can be represented as the sum of two positive integers
- Maximum number of distinct positive integers that can be used to represent N
- Check whether a number can be represented as sum of K distinct positive integers
- Number of arrays of size N whose elements are positive integers and sum is K
- Count positive integers with 0 as a digit and maximum 'd' digits
- Number of n-digits non-decreasing integers
- Find smallest number with given number of digits and sum of digits under given constraints
- Number of integers in a range [L, R] which are divisible by exactly K of it's digits
- Count number of integers less than or equal to N which has exactly 9 divisors
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