Given a string S composed of 0 and 1. Find the minimum splits such that the substring is a binary representation of the power of 4 or 6 with no leading zeros. Print -1 if no such partitioning is possible.
Input: 100110110 Output: 3 The string can be split into a minimum of three substrings 100(power of 4), 110 (power of 6) and 110(power of 6). Input : 00000 Output : -1 0 is not a power of 4 or 6.
A simple solution is to split the string recursively at different indices and check if each split is a power of 4 or 6. Start with index 0 and split str from other string. If it is a power of 4 or 6 then call recursively for index 1 and perform the same operation. When an entire string is split check if a total number of partitions are minimum so far or not. Then split str[0..1], check if it is the power of 4 or 6 and then call recursively for rest string. Compare partitions with minimum so far at the end of string traversal. This approach will be exponential in time.
An efficient solution is to use Dynamic Programming. A 1-D dp table is created in which dp[i] stores minimum number of partitions required to split string str[i..n-1] into substrings that are power of 4 or 6. Suppose we are at index i and str[i..j] is power of 4 or 6, then minimum number of partitions will be minimum number of partitions to split str[j+1..n-1] plus one partition to split str[i..j] from string, that is dp[j+1] + 1. Hence the recurrence relation for (j!=(n-1)) and (dp[j + 1]!=-1) will be:
dp[i] = min(dp[i], dp[j + 1] + 1)
Time Complexity: O(n^2*log(x)), x = largest power of 4 or 6 obtainable from input string.
Auxiliary Space: O(n)
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