Python O(n) sliding window with a lot of comments. Accepted solution

  • 6
    class Solution(object):
        def findAnagrams(self, s, p):
            :type s: str
            :type p: str
            :rtype: List[int]
            hash = {}   # hash stores the list of characters we need to cross-off. Initially has all of p in it
            for c in p:
                if c in hash:
                    hash[c] += 1
                    hash[c] = 1
            count = len(p)  # number of characters still to be crossed-off
            # initialize
            result = []
            left = 0    # the current candidate is s[left:right+1]
            right = 0
            while right < len(s):
                # for every iteration, check if current character is a desired char. if so, cross it off. otherwise, move on to the next character
                if s[right] in hash:
                    hash[s[right]] -= 1
                    if hash[s[right]] >= 0: # If we have a negative hash value(meaning more than enough of that particular character), it means we are not getting any closer to the solution, so, count should not change
                        count -= 1
                # print 'left=', left, 'right=', right, 'count=', count, 'hash=', hash, 'cur_window=', s[left:right+1] 
                # if all items are crossed-off, add to result list
                if count == 0:
                # Move window only if the minimum size is met. 
                if right == left + len(p) - 1:   
                    if s[left] in hash:     # If the char we are getting rid of is already in the hash, increment the hash (add to the items that we need to cross-off)
                        if hash[s[left]]>=0:    # If the hash (number of items we need to cross-off) is negative(i.e we have had double chars in out current window), do not increment the required count
                            count += 1
                        hash[s[left]] += 1
                    left += 1
                right += 1
            return result

  • 0

    great answer! as your can reset the hash value for string p back again.

  • 0

    you can use collections.Counter or hash.get() to simplify the solution.

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