DI String Match.py

'''
Given a string S that only contains "I" (increase) or "D" (decrease), let N = S.length.

Return any permutation A of [0, 1, ..., N] such that for all i = 0, ..., N-1:

If S[i] == "I", then A[i] < A[i+1]
If S[i] == "D", then A[i] > A[i+1]
 

Example 1:

Input: "IDID"
Output: [0,4,1,3,2]
Example 2:

Input: "III"
Output: [0,1,2,3]
Example 3:

Input: "DDI"
Output: [3,2,0,1]
 

Note:

1 <= S.length <= 10000
S only contains characters "I" or "D".
'''

class Solution:
    def diStringMatch(self, S: str) -> List[int]:
        res = [i for i in range(len(S)+1)]
        start = 0
        while start < len(S):
            while start < len(S) and S[start] == 'I':
                start += 1
            
            if start >= len(S):
                break
                
            end = start
            while end < len(S) and S[end] == 'D':
                end += 1
                
            res[start:end+1] = res[start:end+1][::-1]
            
            start = end
        return res