761. Special Binary String

class Solution:
    def makeLargestSpecial(self, s: str) -> str:
        """tc O(N^2)   sc O(N)
        1. keep counting current 1 until cnt == 0, we find partition point,
        2. push substring into stack 
        3. after loop is over, sort the substring and get  lexicographically largest largest string  
        """
        cnt,res = 0, [] 
        l = 0
        split= 0
        for r in range(len(s)):
            if s[r] == '1':
                cnt += 1
            else:
                cnt -= 1
            if cnt == 0:
                split += 1
                res.append('1'+ self.makeLargestSpecial(s[l+1:r]) + '0') # put sorted substring into res 
                l = r + 1 
        #print(len(res),split) #  len === split 
        return ''.join(sorted(res,reverse=True))