human
Give me a Python code to find the minimal balls you have to insert to remove all the balls on the table given the following:
I found an interesting problem on https://leetcode.com/problems/zuma-game/:
Think about Zuma Game. You have a row of balls on the table, colored red(R), yellow(Y), blue(B), green(G), and white(W). You also have several balls in your hand.

Each time, you may choose a ball in your hand, and insert it into the row (including the leftmost place and rightmost place). Then, if there is a group of 3 or more balls in the same color touching, remove these balls. Keep doing this until no more balls can be removed.

Find the minimal balls you have to insert to remove all the balls on the table. If you cannot remove all the balls, output -1.

Examples:
Input: "WRRBBW", "RB"
Output: -1
Explanation: WRRBBW -> WRR[R]BBW -> WBBW -> WBB[B]W -> WW

Input: "WWRRBBWW", "WRBRW"
Output: 2
Explanation: WWRRBBWW -> WWRR[R]BBWW -> WWBBWW -> WWBB[B]WW -> WWWW -> empty

Input:"G", "GGGGG"
Output: 2
Explanation: G -> G[G] -> GG[G] -> empty 

Input: "RBYYBBRRB", "YRBGB"
Output: 3
Explanation: RBYYBBRRB -> RBYY[Y]BBRRB -> RBBBRRB -> RRRB -> B -> B[B] -> BB[B] -> empty 


Note:

You may assume that the initial row of balls on the table won’t have any 3 or more consecutive balls with the same color.
The number of balls on the table won't exceed 20, and the string represents these balls is called "board" in the input.
The number of balls in your hand won't exceed 5, and the string represents these balls is called "hand" in the input.
Both input strings will be non-empty and only contain characters 'R','Y','B','G','W'.

I tried it in Python, but could not do it. Can you solve it?
assistant
#Here is Python code to find the minimal balls you have to insert to remove all the balls on the table.

class Solution:
     def findMinStep(self, board, hand):
         """
         :type board: str
         :type hand: str
         :rtype: int
         """
         res=float("inf")
         hmap=collections.defaultdict(int)
         for c in hand:
             hmap[c]+=1
         res=self.helper(board,hmap)
         if res == float("inf"):
             return -1
         return res
     
     def helper(self,board,hmap):
         board=self.removeConsecutive(board)
         if len(board) ==0:
             return 0
         cnt=float("inf")
         j=0
         for i in range(len(board)+1):
             if i<len(board) and board[i] ==board[j]:
                 continue
             need=3-(i-j)
             if hmap[board[j]]>=need:
                 hmap[board[j]]-=need
                 res=self.helper(board[0:j]+board[i:],hmap)
                 if res!=float("inf"):
                     cnt=min(cnt,res+need)
                 hmap[board[j]]+=need
             j=i
         return cnt
         
     def removeConsecutive(self,board):
         j=0
         for i in range(len(board)+1):
             if i<len(board) and board[i] ==board[j]:
                 continue
             if i-j>=3:
                 return self.removeConsecutive(board[0:j]+board[i:])
             else:
                 j=i
         return board