1487. Making File Names Unique

class Solution:
    def getFolderNames(self, names: List[str]) -> List[str]:
        """ tc O(N) sc O(N)
        1. initialize res, seen as set, a dictionary to record  max cnt for key x has appeared
        2. each time get an entry, extract cnt, and candidate key x
        3. if current candidate key has appeared before, increment cnt by 1 and check if revised key has appeared before untill new key is not used before, update the key 
        4. update set, dictionary's key and value, and update result 
        """
        res = []
        seen = set()
        d =collections.defaultdict(int)   
        for x in names:
            cnt = d[x]#d.get(x,0)   if x not in d before, return 0
            #print(cnt)
            cur = x
            while cur in seen:
                cnt += 1 
                cur = f'{x}({cnt})'
                
            d[x] = cnt
            res.append(cur)
            seen.add(cur)
            
        return res