Given a binary input that represents binary representation of positive number n, find binary representation of smallest number greater than n with same number of 1’s and 0’s as in binary representation of n. If no such number can be formed, print “no greater number”.
The binary input may be and may not fit even in unsigned long long int.
Input : 10010 Output : 10100 Here n = (18)10 = (10010)2 next greater = (20)10 = (10100)2 Binary representation of 20 contains same number of 1's and 0's as in 18. Input : 111000011100111110 Output : 111000011101001111
This problem simply boils down to finding next permutation of a given string. We can find the next_permutation() of the input binary number.
Below is an algorithm to find next permutation in binary string.
- Traverse the binary string bstr from the right.
- While traversing find the first index i such that bstr[i] = ‘0’ and bstr[i+1] = ‘1’.
- Exchange character of at index ‘i’ and ‘i+1’.
- Since we need smallest next value, consider substring from index i+2 to end and move all 1’s in the substring in the end.
Below is the implementation of above steps.
Binary representation of next greater number = 10100
Time Complexity : O(n) where n is number of bits in input.
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