Given a string S consisting of lowercase characters, you have to delete the minimum number of characters from S so that every letter in S appears a unique number of times.
Input: str = “aaaabbbb”
Both ‘a’ and ‘b’ occur 4 times if the first character is deleted then ‘a’ occurs 3 times and ‘b’ occurs 4 times.
Input: str = “geeksforgeeks”
- We can count the frequencies of all 26 possible lower case characters.
- Then construct a map that tells how many letters have a given frequency.
- Iterate the map from higher frequencies to lower.
- If more than 1 letter has a given frequency we delete 1 occurrence of all but 1 letter with that frequency.
- Deleting 1 occurrence of those letters increases the number of the letter that has the frequency one less.
- If the occurrence of a letter is 0 then it is not present in the string.
Below is the implementation of the above approach:
Time Complexity: O(n + m*m), where m = 26.
- Counting the frequency of all characters takes O(N) time where N is the length of S.
- Constructing the map works in O(mlogm) time, where m = 26.
- Deletion works in O(m*m)
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Improved By : ashutosh450