Python3 Program to Find Lexicographically minimum string rotation | Set 1

Write code to find lexicographic minimum in a circular array, e.g. for the array BCABDADAB, the lexicographic minimum is ABBCABDAD.
Source: Google Written Test
More Examples: 

Input:  GEEKSQUIZ
Output: EEKSQUIZG

Input:  GFG
Output: FGG

Input:  GEEKSFORGEEKS
Output: EEKSFORGEEKSG

Following is a simple solution. Let the given string be ‘str’ 
1) Concatenate ‘str’ with itself and store in a temporary string say ‘concat’. 
2) Create an array of strings to store all rotations of ‘str’. Let the array be ‘arr’. 
3) Find all rotations of ‘str’ by taking substrings of ‘concat’ at index 0, 1, 2..n-1. Store these rotations in arr[] 
4) Sort arr[] and return arr[0].

Following is the implementation of above solution. 

Python3

# A simple Python3 program to find lexicographically
# minimum rotation of a given string

# This function return lexicographically minimum
# rotation of str
def minLexRotation(str_) :

    # Find length of given string
    n = len(str_)

    # Create an array of strings to store all rotations
    arr = [0] * n

    # Create a concatenation of string with itself
    concat = str_ + str_

    # One by one store all rotations of str in array.
    # A rotation is obtained by getting a substring of concat
    for i in range(n) :
        arr[i] = concat[i : n + i]

    # Sort all rotations
    arr.sort()

    # Return the first rotation from the sorted array
    return arr[0]

# Driver Code
print(minLexRotation("GEEKSFORGEEKS"))
print(minLexRotation("GEEKSQUIZ"))
print(minLexRotation("BCABDADAB"))

# This code is contributed by divyamohan123

Output:

EEKSFORGEEKSG
EEKSQUIZG
ABBCABDAD

Time complexity of the above solution is O(n²Logn) under the assumption that we have used a O(nLogn) sorting algorithm. 
Please refer complete article on Lexicographically minimum string rotation | Set 1 for more details!

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