Given a number N. The task is to find the number of integers from 1 to n which contains digits 0’s and 1’s only.
Input : N = 15 Output : 3 Explanation : 1, 10, 11 are such integers. Input : N = 120 Output : 7 Explanation : 1, 10, 11, 100, 101, 110, 111 are such integers.
Approach: An efficient approach is to build integers which contain 1’s and 0’s only using a recursive function starting from the number 1. For each number check whether it is less than n or not.
Below is the implementation of the above approach:
- Find the number of positive integers less than or equal to N that have an odd number of digits
- Count of integers in a range which have even number of odd digits and odd number of even digits
- Find the first N integers such that the sum of their digits is equal to 10
- Find smallest number with given number of digits and sum of digits under given constraints
- Find the average of k digits from the beginning and l digits from the end of the given number
- Find the Largest number with given number of digits and sum of digits
- Find the number of integers x in range (1,N) for which x and x+1 have same number of divisors
- Find integers that divides maximum number of elements of the array
- Find maximum number that can be formed using digits of a given number
- Find the smallest number whose digits multiply to a given number n
- Find count of digits in a number that divide the number
- Given a number n, find the first k digits of n^n
- Find first and last digits of a number
- Find M-th number whose repeated sum of digits of a number is N
- Find N digits number which is divisible by D
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