Find Permutation.py

'''
 By now, you are given a secret signature consisting of character 'D' and 'I'. 'D' represents a decreasing relationship between two numbers, 'I' represents an increasing relationship between two numbers. And our secret signature was constructed by a special integer array, which contains uniquely all the different number from 1 to n (n is the length of the secret signature plus 1). For example, the secret signature "DI" can be constructed by array [2,1,3] or [3,1,2], but won't be constructed by array [3,2,4] or [2,1,3,4], which are both illegal constructing special string that can't represent the "DI" secret signature.

On the other hand, now your job is to find the lexicographically smallest permutation of [1, 2, ... n] could refer to the given secret signature in the input.

Example 1:

Input: "I"
Output: [1,2]
Explanation: [1,2] is the only legal initial spectial string can construct secret signature "I", where the number 1 and 2 construct an increasing relationship.

Example 2:

Input: "DI"
Output: [2,1,3]
Explanation: Both [2,1,3] and [3,1,2] can construct the secret signature "DI", 
but since we want to find the one with the smallest lexicographical permutation, you need to output [2,1,3]

Note:
The input string will only contain the character 'D' and 'I'.
The length of input string is a positive integer and will not exceed 10,000
'''



class Solution(object):
    def findPermutation(self, s):
        """
        :type s: str
        :rtype: List[int]
        """
        res = [i + 1 for i in xrange(len(s)+1)]
        
        start = 0
        end = 0
        while start < len(s):
            while start < len(s) and s[start] != 'D':
                start += 1
            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