str.py

class Solution:
    def threeEqualParts(self, A: List[int]) -> List[int]:
        S = ''.join([str(a) for a in A])
        cnt_1 = S.count('1')
        if cnt_1 == 0:return [0, 2]
        # each part should have the same number of '1'
        if cnt_1 % 3!=0:return [-1, -1]
        counter_1, idx, first = 0, 0, ''
        leading_zero = True
        for i, s in enumerate(S):
            if s=='1':
                leading_zero = False
                counter_1 += 1
            if not leading_zero:
                first += s
            if counter_1==cnt_1 //3:
                idx = i
                break
        end_1 = S.rfind('1')
        # Find pending_zero, the final result will be first+pending_zero
        # verify whether each part can match the final result.
        pending_zero = len(S)-1-end_1
        if S[:-pending_zero if pending_zero else len(S)].endswith(first):
            # if contains enough zero for first part to match the pending zero of last part.
            if pending_zero==0 or S[idx+1:].startswith(pending_zero*'0'):
                # verify 1) whether we can find first in the middle 
                #2) whether we have enough zero for second part to match the pending zero of last part
                temp_str = S[idx+1+pending_zero: -(pending_zero+len(first))]
                idx1 = temp_str.find(first)
                if idx1 != -1 and (pending_zero==0 or temp_str.endswith('0'*pending_zero)):
                    ii = idx+pending_zero
                    return [ii, ii+1+idx1+len(first)+pending_zero ]
        return [-1, -1]