Rearrange a string so that all same characters become d distance away
Given a string and a positive integer d. Some characters may be repeated in the given string. Rearrange characters of the given string such that the same characters become d distance away from each other. Note that there can be many possible rearrangements, the output should be one of the possible rearrangements. If no such arrangement is possible, that should also be reported.
The expected time complexity is O(n + m Log(MAX)) Here n is the length of string, m is the count of distinct characters in a string and MAX is the maximum possible different characters.
Input: "abb", d = 2 Output: "bab" Input: "aacbbc", d = 3 Output: "abcabc" Input: "geeksforgeeks", d = 3 Output: egkegkesfesor Input: "aaa", d = 2 Output: Cannot be rearranged
The approach to solving this problem is to count frequencies of all characters and consider the most frequent character first and place all occurrences of it as close as possible. After the most frequent character is placed, repeat the same process for the remaining characters.
- Let the given string be str and size of string be n
- Traverse str, store all characters and their frequencies in a Max Heap MH(implemented using priority queue). The value of frequency decides the order in MH, i.e., the most frequent character is at the root of MH.
- Make all characters of str as ‘\0’.
- Do the following while MH is not empty.
- Extract the Most frequent character. Let the extracted character be x and its frequency be f.
- Find the first available position in str, i.e., find the first ‘\0’ in str.
- Let the first position be p. Fill x at p, p+d,.. p+(f-1)d
Below is the implementation of the above algorithm.
Algorithmic Paradigm: Greedy Algorithm
Time Complexity: Time complexity of above implementation is O(n + mLog(MAX)). Here n is the length of str, m is the count of distinct characters in str and MAX is the maximum possible different characters.
Auxiliary Space : O(N)