Leetcode-question-Longest-Repeating-Character-Replacement.py

def characterReplacement(self, s: str, k: int) -> int: 
        d={} #to calculate the frquency of elements present in the particular substring or sliding window
        a=0 #for counting the length of the longest substring
        l=0 #the left pointer (starts from the left index of the s)
        for r in range(len(s)): # r is taken as the right pointer and it will go to the end of the substring or sliding window which will be chosen
            #now calulating te frequency of the elements present in the particular chosen substring
            if s[r] in d: 
                d[s[r]]+=1 
            else: 
                d[s[r]]=1 
            #now checking how many less fequency element present in d so that it can be replaced and converted to the max frequency element
            # (r-l+1) indicates the total length of the sliding window chosen
            #max(d.values() it takes the maximum frequency element so that after subtracting
            #it from the length of the sliding window can give how many elements need to
            #be converted into max frequency elements (it should be greater than k)
            while (r-l+1)-max(d.values()) >k: 
                #if greater than k then the current window will move one step forward and 
                #the starting of the element of the window need to be decrement by 1
                #as its frequency will decrement once its gone from window
                d[s[l]]-=1
                l+=1 
                #moving forward the left pointer(shifting window forward) 
            #a storing the length of longest substring
            a=max(a,r-l+1) 
        return a