Convert to a string that is repetition of a substring of k length - GeeksforGeeks


Convert to a string that is repetition of a substring of k length - GeeksforGeeks
Given a string, find if it is possible to convert it to a string that is repetition of substring with k characters. To convert, we can replace one substring of length k with k characters.



One observation is, length of string must be a multiple of k as we can replace only one substring.
The idea is declare a map mp which maps strings of length k to an integer denoting its count. So, if there are only two different sub-strings of length k in the map container and count of one of the sub-string is 1 then answer is true. Otherwise answer is false.

bool checkString(string str, long k)
{
    // Length of string must be a multiple of k
    int n = str.length();
    if (n%k != 0)
        return false;
 
    // Map to store strings of length k and their counts
    unordered_map<string, int> mp;
    for (int i=0; i<n; i+=k)
        mp[str.substr(i, k)]++;
 
    // If string is already a repition of k substrings,
    // return true.
    if (mp.size() == 1)
        return true;
 
    // If number of distinct substrings is not 2, then
    // not possible to replace a string.
    if (mp.size() != 2)
        return false;
 
    // One of the two distinct must appear exactly once.
    // Either the first entry appears once, or it appears
    // n/k-1 times to make other substring appear once.
    if ((mp.begin()->second == (n/k - 1)) ||
                    mp.begin()->second == 1)
       return true;
 
    return false;
}
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