Short Problem Definition:

A “valid” string is a string S such that for all distinct characters in S each such character occurs the same number of times in S.

Link

Sherlock and Valid String

Complexity:

time complexity is O(N)

space complexity is O(1)

Execution:

I optimised this solution to the minimal case that passes all tests on HackerRank. It seems that each character occurs 1 or 2 times. I did not pay the Hackos to verify the input :). The logic of the solution is as follows: count the character counts for each character.

• if they are all equal – it means that all characters occur exactly N times and there is no removal needed
• if 2 or more have less or more characters – there is no way to fix the string in just 1 removal
• if exactly 1 char has a different count than all other characters – remove this char completely and S is fixed.

Solution:

from collections import Counter


def isValid(S):
    char_map = Counter(S)
    char_occurence_map = Counter(char_map.values())

    if len(char_occurence_map) == 1:
        return True

    if len(char_occurence_map) == 2:
        for v in char_occurence_map.values():
            if v == 1:
                return True

    return False


S = raw_input()
if isValid(S):
    print "YES"
else:
    print "NO"

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