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Python Program to find minimum number of rotations to obtain actual string

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Given two strings s1 and s2. The task is to find out the minimum number of string rotations for the given string s1 to obtain the actual string s2. Examples:

Input : eeksg, geeks
Output: 1 
Explanation: g is rotated left to obtain geeks.

Input : eksge, geeks
Output: 2
Explanation : e and g are left rotated to obtain geeks.

Approach:

  • Use string slicing to rotate the string.
  • Perform right rotations str1=str1[1:len(str1)]+str1[0] on string to obtain the actual string.
  • Perform left rotations m=m[len(m)-1]+m[:len(m)-1] on string to obtain the actual string.
  • Print the minimum of left(x) and right(y) rotations.

TIME COMPLEXITY: O(n) Below is the implementation: 

python3

def findRotations(str1, str2):
     
    # To count left rotations
    # of string
    x = 0
     
    # To count right rotations
    # of string
    y = 0
    m = str1
     
    while True:
         
        # left rotating the string
        m = m[len(m)-1] + m[:len(m)-1]
         
        # checking if rotated and
        # actual string are equal.
        if(m == str2):
            x += 1
            break
             
        else:
            x += 1
            if x > len(str2) :
                break
  
    while True:
         
        # right rotating the string
        str1 = str1[1:len(str1)]+str1[0]
         
        # checking if rotated and actual
        # string are equal.
        if(str1 == str2):
            y += 1
            break
             
        else:
            y += 1
            if y > len(str2):
                break
                 
    if x < len(str2):
         
        # printing the minimum
        # number of rotations.
        print(min(x,y))
         
    else:
        print("given strings are not of same kind")
         
# Driver code
findRotations('sgeek', 'geeks')

                    
Output:
1

The Time and Space Complexity for all the methods are the same:

Time Complexity: O(n)

Auxiliary Space: O(n)



Last Updated : 09 Sep, 2022
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